Ruby macos kokoro environment and package build updates

Rakefile

@@ -99,7 +99,7 @@ task 'dlls' do
     env_comp = "CC=#{opt[:cross]}-gcc "
     env_comp += "CXX=#{opt[:cross]}-g++ "
     env_comp += "LD=#{opt[:cross]}-gcc "
-    docker_for_windows "gem update --system && #{env} #{env_comp} make -j #{out} && #{opt[:cross]}-strip -x -S #{out} && cp #{out} #{opt[:out]}"
+    docker_for_windows "gem update --system --no-ri --no-doc && #{env} #{env_comp} make -j #{out} && #{opt[:cross]}-strip -x -S #{out} && cp #{out} #{opt[:out]}"
   end
 
 end
@@ -113,10 +113,15 @@ task 'gem:native' do
   if RUBY_PLATFORM =~ /darwin/
     FileUtils.touch 'grpc_c.32.ruby'
     FileUtils.touch 'grpc_c.64.ruby'
+    unless '2.5' == /(\d+\.\d+)/.match(RUBY_VERSION).to_s
+      fail "rake gem:native (the rake task to build the binary packages) is being " \
+        "invoked on macos with ruby #{RUBY_VERSION}. The ruby macos artifact " \
+        "build should be running on ruby 2.5."
+    end
     system "rake cross native gem RUBY_CC_VERSION=2.5.0:2.4.0:2.3.0:2.2.2:2.1.6:2.0.0 V=#{verbose} GRPC_CONFIG=#{grpc_config}"
   else
     Rake::Task['dlls'].execute
-    docker_for_windows "gem update --system && bundle && rake cross native gem RUBY_CC_VERSION=2.5.0:2.4.0:2.3.0:2.2.2:2.1.6:2.0.0 V=#{verbose} GRPC_CONFIG=#{grpc_config}"
+    docker_for_windows "gem update --system --no-ri --no-doc && bundle && rake cross native gem RUBY_CC_VERSION=2.5.0:2.4.0:2.3.0:2.2.2:2.1.6:2.0.0 V=#{verbose} GRPC_CONFIG=#{grpc_config}"
   end
 end
 

tools/internal_ci/helper_scripts/prepare_build_macos_rc

@@ -50,7 +50,8 @@ 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 use ruby-2.4
+rvm install 2.5.0
+rvm use 2.5.0 --default
 rvm osx-ssl-certs status all
 rvm osx-ssl-certs update all
 set -ex