phase1,phase2: shuffle order of builds

phase1,phase2: shuffle order of builds

It seems that once there are new commits, buildbot restarts building all
targets in alphabetical order. The current logic pretty much disables
the building of the alphabetically last targets, so until there is
proper solution just workaround it by randomly shuffling the builders
list.

References: https://github.com/buildbot/buildbot/issues/5193
Signed-off-by: Petr Štetiar <ynezz@true.cz>