Merge pull request #21203 from jtattermusch/fix_pip_install_commands

fix pip install commands

tools/internal_ci/helper_scripts/prepare_build_macos_rc

@@ -20,7 +20,7 @@ launchctl limit maxfiles
 ulimit -a
 
 # Add GCP credentials for BQ access
-pip install google-api-python-client oauth2client --user python
+pip install --user google-api-python-client oauth2client
 export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/GrpcTesting-d0eeee2db331.json
 
 # If this is a PR using RUN_TESTS_FLAGS var, then add flags to filter tests
@@ -50,8 +50,8 @@ mkdir -p ~/.cocoapods/repos
 time git clone --depth 1 https://github.com/CocoaPods/Specs.git ~/.cocoapods/repos/master
 
 # python
-time pip install virtualenv --user python
-time pip install -U Mako six tox setuptools twisted pyyaml pyjwt cryptography requests --user python
+time pip install --user virtualenv
+time pip install --user --upgrade Mako six tox setuptools twisted pyyaml pyjwt cryptography requests
 export PYTHONPATH=/Library/Python/3.4/site-packages
 
 # Install Python 3.7