Check per janitor run

Created by: rafax

Do one "is the right shard" check per janitor run (instead of one per repo) to:

• do less work
• log less failures (this error case is not really repo specific)
• have an easy way of checking match between hostname and full Kubernetes endpoint address

Also, group wrongShard tests.

Test plan

• unit tests
• local testing with 2 gitserver replicas