rebootstrap: for now, trigger builds on every commit to rebootstrat.git and every sunday at 11/12:55
send irc notifications about rebootstrap jobs to #debian-bootstrap
rebootstrap: track different branch

By using a separate branch for jenkins, I can still push changes to
master while selectively triggering jenkins by pushes to that branch
thus saving resources.
rebootstrap: add gcc-4.9 flavour for arm64
add logparse rules for rebootstrap
fix description of rebootstrap_arm64_gcc49
rebootstrap: limit concurrent rebootstrap jobs to 2 and schedule them with slightly less than default (=100) priority
add rebootstrap jobs for x32 and arm64-multilib
try once again to configure email for lintian-tests as we want it
remove useless gitrepo variable