Add Gemfile.lock/bundler checking

This commit adds a little helper script post-checkout to determine if
the Gemfile dependencies are still valid post-checkout. If they
aren't, the script will give a little warning. This should hopefully
remove a little bit of friction and annoyance when updating the
repository.

Change-Id: I6ebe97a926d170914604594637985cec7eb2a519
Reviewed-on: https://gerrit.causes.com/29509
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Greg Hurrell <greg@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>