Allow HF build from testing branch

Currently it is not possible to build a HF package from a testing branch but only from the maintenance ones.

Ideally 2 distinct parameters should be provided:

1. a target branch (for example a maintenance branch like 10.10)
2. a testing branch (for example a branch pulled from 10.10 with some commit to test)

The rest of the build should be identical to the following job:
https://qa2.nuxeo.org/jenkins/view/HF%20nightly/job/IT-HF-pkg-build-nightly-ondemand/