Various Ruby cartridge improvements

* Refactored httpd start in control script
* Fixed wrong return code from gemfile_is_modified() to handle first git push
* Prevent running bundle install --deployment when there was no modification to a Gemfile/Gemfile.lock in git push.
* Prevent running `bundle exec rake -T` to check if there is a 'assets:precompile' if there is no `rails` in Gemfile (speed up deployment of non-Rails applications)