Bug 1005123

Move deletion of checksum file for Gemfile.lock from pre-repo-archive to
build because pre-repo-archive isn't invoked when using a builder
cartridge, meaning that force_clean_build wouldn't always be respected.

Update the checksum file if it changes, so future checksum comparisons
will evaluate correctly.
Merge pull request #4572 from ncdc/bugs/1005123-ruby-jenkins-force-clean-build-broken

Merged by openshift-bot