[JENKINS-14026] DefaultBuildChooser should handle smartly branches with /

When encountering a single branch containing a '/', it is either a qualified branch or a branch containing a '/'
In the first case, the branch should start with the name of a declared remote
Otherwise, we fall back to unqualified behaviour, and we try to match the branch name as if it was */BRANCH
Merge pull request #195 from Vlatombe/JENKINS-14026

[JENKINS-14026] DefaultBuildChooser should handle smartly branches with /