update gem installation checks in test script

Author: sireeshajonnalagadda

test/ruby-rails-postgres/test.sh

@@ -15,7 +15,10 @@ check "rails" rails --version
 check "rails installation path" gem which rails
 check "user has write permission to rvm gems" [ -w /usr/local/rvm/gems ]
 check "user has write permission to rvm gems default" [ -w /usr/local/rvm/gems/default ]
-check "user can install gems" gem install github-markup
+# Verify bundler is available in the gem list
+check "user can install gems" gem list | grep -q bundler
+# Verify user can successfully install a gem package
+check "user can install gems" gem install json --no-document
 
 # Report result
 reportResults