phase1: AnyBranchScheduler: make treeStableTimer configurable

phase1: AnyBranchScheduler: make treeStableTimer configurable

The AnyBranchScheduler will currently wait for 15 minutes before
starting a build.  If new changes are made on the same branch during
this interval, the timer will be restarted.

For staging repository we want faster feedback loop, so we're going to
use much lower value, thus lets make this configurable and handled via
Ansible.

Signed-off-by: Petr Štetiar <ynezz@true.cz>