Merge pull request #12014 from jtattermusch/kokoro_populate_xdg

Pre-populate xdg-cache-home to deflake python kokoro build

tools/internal_ci/helper_scripts/prepare_build_linux_rc

@@ -24,6 +24,10 @@ ulimit -n 32768
 echo 'DOCKER_OPTS="${DOCKER_OPTS} --graph=/tmpfs/docker"' | sudo tee --append /etc/default/docker
 sudo service docker restart
 
+# Populate xdg-cache-home to workaround https://github.com/grpc/grpc/issues/11968
+sudo mkdir -p /tmp/xdg-cache-home
+PYTHONWARNINGS=ignore XDG_CACHE_HOME=/tmp/xdg-cache-home sudo -E pip install coverage==4.4
+
 # Download Docker images from DockerHub
 export DOCKERHUB_ORGANIZATION=grpctesting