Create an easier way to specify omnibus branch on triggered build
Related to #2234 (closed)
When build is triggered from CE, pointing to the non master
branch of omnibus-gitlab repository is a bit more involved https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/build_test_package.md .
We should find an easier way to do this so that the triggered build is even simpler.
For example, maybe we should create a rule where your branch name in CE and the change you are doing in omnibus should be the same. If the branch does not exist in omnibus-gitlab, default to master.