jenkins: extract common parts of build scripts to separate file

Have all complexity in one common shell script, greatly simplify the individual
scripts.

This allows to provide a specific branch or git hash to build instead of
current master. Some scripts allowed to provide branch names before, this now
also allows using git hashes directly.

Environment variables can be used to override the git hash/branch to use for
specific repositories.

Motivation for this patch: we need this to investigate failure causes more
easily.

Change-Id: I5ac2f90d006a1b2f6c246976346d852a70c89089
6 files changed