update macos kokoro rc script

tools/internal_ci/helper_scripts/prepare_build_macos_rc

@@ -15,53 +15,29 @@
 
 # Source this rc script to prepare the environment for macos builds
 
-# TODO(jtattermusch): remove all deps once installed on MacOS workers
+# required to build protobuf
+brew install gflags
 
-# brew and C++ deps
-yes | ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
-brew install autoconf automake libtool ccache cmake gflags gpg wget
-
-# TODO(jtattermusch): hkp://keys.gnupg.net fails with "No route to host"
-gpg --keyserver hkp://193.164.133.100 --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3
-curl -sSL https://get.rvm.io | sudo bash -s stable
-
-# add ourselves to rvm group to prevent later "access denied" errors.
-sudo dseditgroup -o edit -a `whoami` -t user rvm
-
-set +ex
-source /etc/profile.d/rvm.sh
+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 ruby-2.3
-gem install bundler
-
 rvm osx-ssl-certs status all
 rvm osx-ssl-certs update all
 set -ex
 
+gem install bundler
+
 # cocoapods
-gem install cocoapods --version 1.0.0
+export LANG=en_US.UTF-8
+gem install cocoapods
+pod repo update  # needed by python
 
 # python
-wget -q https://bootstrap.pypa.io/get-pip.py
-sudo python get-pip.py
+brew install coreutils  # we need grealpath
+#wget -q https://bootstrap.pypa.io/get-pip.py
+#sudo python get-pip.py
 sudo pip install virtualenv
-
-# TODO(jtattermusch): install python3
-
-# mono
-wget -q https://download.mono-project.com/archive/5.0.1/macos-10-universal/MonoFramework-MDK-5.0.1.1.macos10.xamarin.universal.pkg
-sudo installer -pkg MonoFramework-MDK-5.0.1.1.macos10.xamarin.universal.pkg -target /
-ln -s /Library/Frameworks/Mono.framework/Versions/Current/bin/mono /usr/local/bin/mono
- 
-# dotnet SDK
-brew install openssl
-wget -q https://go.microsoft.com/fwlink/?linkid=843444 -O dotnet-dev-osx-x64.1.0.1.pkg
-sudo installer -pkg dotnet-dev-osx-x64.1.0.1.pkg -target /
-ln -s /usr/local/share/dotnet/dotnet /usr/local/bin/dotnet
-dotnet --version  # bootstrap dotnet SDK
-
-# nvm
-wget -qO- https://raw.githubusercontent.com/creationix/nvm/v0.30.2/install.sh | bash
-
-# TODO(jtattermusch): install node if needed
+sudo pip install -U six tox setuptools
 
 git submodule update --init