Bazel rules for Python grpcio_health_checking

Add Bazel rules for building and testing grpcio_health_checking.

An unofficial fork for rules_protobuf is used for now as it incorporates
a change (#196 by duduko on the upstream repo pubref/rules_protobuf)
which allows the protoc compiler to compile generated protos too. This
was not merged because the change was failing for golang, but works as
expected for Python.

This is needed because grpcio_health_checking fetches it's proto file
from a different directory (previously achived through setup.py) and
thus needs to be moved to the required location within bazel-genfiles
using a genrule.

WORKSPACE

@@ -34,10 +34,11 @@ pip_import(
 load("@grpc_python_dependencies//:requirements.bzl", "pip_install")
 pip_install()
 
+# NOTE(https://github.com/pubref/rules_protobuf/pull/196): Switch to upstream repo after this gets merged.
 git_repository(
     name="org_pubref_rules_protobuf",
-    remote="https://github.com/pubref/rules_protobuf",
-    tag="v0.8.2",
+    remote="https://github.com/ghostwriternr/rules_protobuf",
+    tag="v0.8.2.1-alpha",
 )
 
 load("@org_pubref_rules_protobuf//python:rules.bzl", "py_proto_repositories")

src/proto/grpc/health/v1/BUILD

@@ -22,3 +22,11 @@ grpc_proto_library(
     name = "health_proto",
     srcs = ["health.proto"],
 )
+
+filegroup(
+    name = "health_proto_file",
+    srcs = [
+        "health.proto",
+    ],
+)
+

src/python/grpcio_health_checking/grpc_health/v1/BUILD.bazel

@@ -0,0 +1,33 @@
+load("@grpc_python_dependencies//:requirements.bzl", "requirement")
+load("@org_pubref_rules_protobuf//python:rules.bzl", "py_proto_library")
+
+package(default_visibility = ["//visibility:public"])
+
+genrule(
+    name = "mv_health_proto",
+    srcs = [
+        "//src/proto/grpc/health/v1:health_proto_file",
+    ],
+    outs = ["health.proto",],
+    cmd = "cp $< $@",
+)
+
+py_proto_library(
+    name = "py_health_proto",
+    protos = [":mv_health_proto",],
+    with_grpc = True,
+    deps = [
+        requirement('protobuf'),
+    ],
+)
+
+py_library(
+    name = "grpc_health",
+    srcs = ["health.py",],
+    deps = [
+        ":py_health_proto",
+        "//src/python/grpcio/grpc:grpcio",
+    ],
+    imports=["../../",],
+)
+

src/python/grpcio_tests/tests/health_check/BUILD.bazel

@@ -0,0 +1,15 @@
+package(default_visibility = ["//visibility:public"])
+
+py_test(
+    name = "health_servicer_test",
+    srcs = ["_health_servicer_test.py"],
+    main = "_health_servicer_test.py",
+    size = "small",
+    deps = [
+        "//src/python/grpcio/grpc:grpcio",
+        "//src/python/grpcio_health_checking/grpc_health/v1:grpc_health",
+        "//src/python/grpcio_tests/tests/unit:test_common",
+    ],
+    imports = ["../../",],
+)
+