The systemd healthcheck timer first triggers 120s after activation.
The initial value for ExecMainStatus is 0, resulting in false positives if we
check this too early.
This changes waits (up to 5 mins) for ExecMainPID to be set and the service to
return to an inactive/failed state.
Change-Id: Iad4ebb283a7a6559b6fffead4145cc9bbad45e4e
Depends-On: Ia2897a6be3e000a9594103502b716431baa615b1
Related-bug: #1843555
c919f1b65b