Fix linker error on objc mac tests by explicitly installing cocoapods v1.3.1, rather than picking up 1.4.1

src/objective-c/GRPCClient/private/GRPCChannel.m

@@ -189,6 +189,7 @@ static grpc_channel_args *BuildChannelArgs(NSDictionary *dictionary) {
     timeout = 0;
   }
   grpc_slice host_slice;
+  memset(&host_slice, 0, sizeof(host_slice));
   if (serverName) {
     host_slice = grpc_slice_from_copied_string(serverName.UTF8String);
   }

test/core/end2end/tests/streaming_error_response.cc

@@ -111,7 +111,7 @@ static void test(grpc_end2end_test_config config, bool request_status_early) {
   grpc_byte_buffer* response_payload1_recv = nullptr;
   grpc_byte_buffer* response_payload2_recv = nullptr;
   grpc_call_details call_details;
-  grpc_status_code status;
+  grpc_status_code status = GRPC_STATUS_OK;
   grpc_call_error error;
   grpc_slice details;
   int was_cancelled = 2;

tools/internal_ci/helper_scripts/prepare_build_macos_rc

@@ -50,8 +50,11 @@ fi
 set +ex  # rvm script is very verbose and exits with errorcode
 source $HOME/.rvm/scripts/rvm
 set -e  # rvm commands are very verbose
-rvm install 2.5.0
+time rvm install 2.5.0
 rvm use 2.5.0 --default
+gem install bundler --no-ri --no-doc
+gem install cocoapods --version 1.3.1 --no-ri --no-doc
+gem install rake-compiler --no-ri --no-doc
 rvm osx-ssl-certs status all
 rvm osx-ssl-certs update all
 set -ex