add instruction to add cacerts/roots.pem to grpc/php docker image in gce_setup

tools/dockerfile/grpc_php/Dockerfile

@@ -48,6 +48,13 @@ RUN cd /var/local/git/grpc/src/php/ext/grpc \
 
 RUN cd /var/local/git/grpc/src/php && composer install
 
+# Add a cacerts directory containing the Google root pem file, allowing the
+# php client to access the production test instance
+ADD cacerts cacerts
+
+# Add a service_account directory containing the auth creds file
+ADD service_account service_account
+
 RUN cd /var/local/git/grpc/src/php && protoc-gen-php -i tests/interop/ -o tests/interop/ tests/interop/test.proto
 
-RUN cd /var/local/git/grpc/src/php && ./bin/run_tests.sh
\ No newline at end of file
+RUN cd /var/local/git/grpc/src/php && ./bin/run_tests.sh

tools/gce_setup/shared_startup_funcs.sh

@@ -421,6 +421,10 @@ grpc_dockerfile_install() {
     grpc_docker_sync_roots_pem $dockerfile_dir/cacerts || return 1;
     grpc_docker_sync_service_account $dockerfile_dir/service_account || return 1;
   }
+  [[ $image_label == "grpc/php" ]] && {
+    grpc_docker_sync_roots_pem $dockerfile_dir/cacerts || return 1;
+    grpc_docker_sync_service_account $dockerfile_dir/service_account || return 1;
+  }
   [[ $image_label == "grpc/cxx" ]] && {
     grpc_docker_sync_roots_pem $dockerfile_dir/cacerts || return 1;
     grpc_docker_sync_service_account $dockerfile_dir/service_account || return 1;