Instead of having separate templates for each branch, use a single
template - together with a neutron variant - for the stable periodic
jobs and add the required branch conditions here.
Once this is in, we can use it in project-config.
Needed-By: I41e2325fa98d2e5575a745a3f438fad2c4075ae8
Change-Id: I6167dceee27db0d17f2febd52e85224ac6df1eac
15e7a736ee