[Android compile server] Fixes
[Android compile server] Fixes

* Only respond to OBJECT_FINALIZE (new object) events.
* Swap checks for if mirror is running and if checkouts are all busy, otherwise it is confusing.

Bug: skia:9302
Change-Id: I51b063967c739428ce7b09cb4961bdb072f35704
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/233461
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot