Make Node interop tests use c-core changes

tools/dockerfile/interoptest/grpc_interop_node/build_interop.sh

@@ -17,12 +17,23 @@
 set -e
 
 mkdir -p /var/local/git
+
 git clone /var/local/jenkins/grpc-node /var/local/git/grpc-node
 # clone gRPC submodules, use data from locally cloned submodules where possible
 (cd /var/local/jenkins/grpc-node/ && git submodule foreach 'cd /var/local/git/grpc-node \
 && git submodule update --init --recursive --reference /var/local/jenkins/grpc-node/${name} \
 ${name}')
 
+# Use the pending c-core changes if possible
+if [ -d "/var/local/jenkins/grpc" ]; then
+  cd /var/local/jenkins/grpc
+  CURRENT_COMMIT="$(git rev-parse --verify HEAD)"
+  cd /var/local/git/grpc-node/packages/grpc-native-core/deps/grpc/
+  git fetch --tags --progress https://github.com/grpc/grpc.git +refs/pull/*:refs/remotes/origin/pr/*
+  git checkout $CURRENT_COMMIT
+  git submodule update --init --recursive --reference /var/local/jenkins/grpc
+fi
+
 # copy service account keys if available
 cp -r /var/local/jenkins/service_account $HOME || true