message: Use easy_install for pip installation for RBE images.
  We will remove python-pip deb packages from rbe-{debian8, ubuntu16_04}:
  So that we don't we have pip install by deb packages and Python's own package system (and they conflict with each other)
  We only install pip by easy_install.
diff: @@ -20,8 +20,8 @@ if [ ! -f /usr/bin/x86_64-linux-gnu-gcc ]; then
  ln -s /usr/local/bin/clang /usr/bin/x86_64-linux-gnu-gcc
  fi
  -pip2 install --upgrade setuptools
  -pip3 install --upgrade setuptools
  +easy_install -U pip==9.0.3
  +easy_install3 -U pip==9.0.3
  # The rest of the pip packages will be installed in
  # `install_pip_packages.sh`
  