Update the brew workflow

- Remove the `brew install`; the kokoro image already has it, just
  update/upgrade instead.
- Remove `prune`, logs had:
    """
    Error: Unknown command: prune
    """
- Remove `uninstall`, logs had:
    """
    Error: Refusing to uninstall /usr/local/Cellar/cmake/3.16.4 and /usr/local/Cellar/icu4c/64.2
    because they are required by ceres-solver, ffmpeg, harfbuzz, libass and opencv, which are currently installed.
    You can override this and force removal with:
      brew uninstall --ignore-dependencies node icu4c cmake wget
    """
- Skip installing some things since they are already in the base image, logs
  had:
    """
    Warning: gflags 2.2.2 is already installed and up-to-date
    To reinstall 2.2.2, run `brew reinstall gflags`
    Warning: openssl@1.1 1.1.1g is already installed and up-to-date
    To reinstall 1.1.1g, run `brew reinstall openssl@1.1`
    Warning: pcre 8.44 is already installed and up-to-date
    To reinstall 8.44, run `brew reinstall pcre`
    """
- Don't install gpg gpg2 as gnupg is already installed, also use gpg instead of
  gpg2 for commands (and update the commands), logs had:
    """
    kokoro/macos/prepare_build_macos_rc: line 44: gpg2: command not found
    kokoro/macos/prepare_build_macos_rc: line 45: gpg2: command not found
    """
- Add env guards to control all the option installs and only request them be
  installed in the cases that need it.  This avoids having to install/update
  the things like ruby when some other tool only needed in some configs is
  install differently and could have conflicts.
- Switch to brew for cocoapods to avoid compat issues on the supporting
  libraries.

kokoro/macos/objectivec_cocoapods_integration/build.sh

@@ -6,6 +6,7 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_COCOAPODS=yes
 source kokoro/macos/prepare_build_macos_rc
 
 ./tests.sh objectivec_cocoapods_integration

kokoro/macos/prepare_build_macos_rc

@@ -2,6 +2,8 @@
 #
 # This script sets up a Kokoro MacOS worker for running Protobuf tests
 
+set -eux
+
 ##
 # Select Xcode version
 
@@ -18,24 +20,61 @@ export CC=gcc
 export CXX=g++
 
 ##
-# Install Brew and core softwares
+# Brew: update, then upgrade the installed tools to current version and install
+# some needed ones not in the Kokoro base image. This ensure current versions
+# of CMake, autotools, etc.
+
+# But first...
+#
+# The transitive deps of the installed tools need protobuf, but Kokoro manually
+# installed it outside of brew so it needs to be removed so brew can install the
+# tools (and a newer version of protobuf). g/kokoro-users/7FRvQMUdN40 about why
+# it is a manual install vs. a brew install in the first place.
+sudo rm -rf \
+    /usr/local/include/google/protobuf \
+    /usr/local/bin/protoc
+# Likewise, updating python can have issues because of some existing binaries.
+sudo rm -rf \
+    /usr/local/bin/2to3* \
+    /usr/local/bin/idle3* \
+    /usr/local/bin/pydoc3* \
+    /usr/local/bin/python3* \
+    /usr/local/bin/pyvenv*
+
+brew update
+brew upgrade
+
+##
+# Install Ruby
 
-ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
-source $HOME/.rvm/scripts/rvm
-brew uninstall node icu4c cmake wget
-brew prune
-brew install gflags gpg gpg2 node openssl pcre ruby cmake wget
-sudo chown -R $(whoami) /usr/local
-brew postinstall node
+if [[ "${KOKORO_INSTALL_RUBY:-}" == "yes" ]] ; then
+  brew install ruby
+fi
+
+##
+# Install Cocoapods
+
+if [[ "${KOKORO_INSTALL_COCOAPODS:-}" == "yes" ]] ; then
+  # The existing cocoapods was installed via gem, but that doesn't work well
+  # with the overlap in deps with things managed by brew (errors around ruby
+  # versions, etc.); so remove it and install in via brew instead.
+  gem uninstall -a "$(gem list | grep cocoapods | cut -d ' ' -f 1)"
+  brew install cocoapods
+fi
 
 ##
 # Install Tox
 
-sudo pip install tox==2.4.1
+if [[ "${KOKORO_INSTALL_TOX:-}" == "yes" ]] ; then
+  sudo pip install tox==2.4.1
+fi
 
 ##
 # Install RVM
 
-gpg2 --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
-command curl -sSL https://rvm.io/mpapis.asc | gpg2 --import -
-curl -sSL https://get.rvm.io | bash -s stable --ruby
+if [[ "${KOKORO_INSTALL_RVM:-}" == "yes" ]] ; then
+  curl -sSL https://rvm.io/mpapis.asc | gpg --import -
+  curl -sSL https://rvm.io/pkuczynski.asc | gpg --import -
+
+  curl -sSL https://get.rvm.io | bash -s stable --ruby
+fi

kokoro/macos/python/build.sh

@@ -6,6 +6,7 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_TOX=yes
 source kokoro/macos/prepare_build_macos_rc
 
 ./tests.sh python

kokoro/macos/python_cpp/build.sh

@@ -6,6 +6,7 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_TOX=yes
 source kokoro/macos/prepare_build_macos_rc
 g++ --version
 

kokoro/macos/ruby23/build.sh

@@ -6,6 +6,8 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_RUBY=yes
+KOKORO_INSTALL_RVM=yes
 source kokoro/macos/prepare_build_macos_rc
 
 ./tests.sh ruby23

kokoro/macos/ruby24/build.sh

@@ -6,6 +6,8 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_RUBY=yes
+KOKORO_INSTALL_RVM=yes
 source kokoro/macos/prepare_build_macos_rc
 
 ./tests.sh ruby24

kokoro/macos/ruby25/build.sh

@@ -6,6 +6,8 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_RUBY=yes
+KOKORO_INSTALL_RVM=yes
 source kokoro/macos/prepare_build_macos_rc
 
 ./tests.sh ruby25

kokoro/macos/ruby26/build.sh

@@ -6,6 +6,8 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_RUBY=yes
+KOKORO_INSTALL_RVM=yes
 source kokoro/macos/prepare_build_macos_rc
 
 ./tests.sh ruby26

kokoro/macos/ruby27/build.sh

@@ -6,6 +6,8 @@
 cd $(dirname $0)/../../..
 
 # Prepare worker environment to run tests
+KOKORO_INSTALL_RUBY=yes
+KOKORO_INSTALL_RVM=yes
 source kokoro/macos/prepare_build_macos_rc
 
 ./tests.sh ruby27

tests.sh

@@ -305,8 +305,6 @@ build_objectivec_tvos_release() {
 }
 
 build_objectivec_cocoapods_integration() {
-  # Update pod to the latest version.
-  gem install cocoapods --no_document
   objectivec/Tests/CocoaPods/run_tests.sh
 }