Bug 1575471 - Properly report the beginning of automation tiers. r=nalexander

Bug 1575471 - Properly report the beginning of automation tiers. r=nalexander

The automation tiers all have a dependency:
  automation/%: automation-start/%

The dependency runs the command for BUILDSTATUS, making the resource
monitor aware of what tiers start. Unfortunately, Make decides to run
all these automation-start/% targets way before starting the
automation/% targets, because of how the interdependencies are laid out.

Use a slightly better way, albeit still biased, making the
automation-start/% target for a tier depend on the dependencies, which
at least ensures that the resource monitor doesn't see a tier starting
before its dependencies are finished.

Differential Revision: https://phabricator.services.mozilla.com/D42805

--HG--
extra : moz-landing-system : lando