Fix gate job timing issues with bundler

Make ruby bundler in gate more resilient by only running
one job rather then multiple jobs in parallel and retry
the bundler install operation 3 times rather then failing
after first attempt for git requests and network issues.

* Use --jobs 1
* Use --retry 3
* Use --verbose to help with extension compile debugging
These are documented here: http://bundler.io/v1.5/bundle_install.html

Change-Id: Ic93ba6e7487ed92aa9cb984b6b8e7df08959b2aa
Closes-Bug: #1357439
Merge "Fix gate job timing issues with bundler"