Add a max timeout in checkpoint_gc

After one hour, we will abandon our efforts to do checkpointing ahead of
time. At that point, it's likely that something has gone wrong with
garbage collection. Log dirty segments.

Test: Run checkpoint_gc after remounting with checkpoint=disable. This
      will prevent GC from making progress. The script should exit after
      one hour
Bug: 131557838

Change-Id: Ifbff5d3e889725259d7c797fe6fa1d4a84fc7cec
1 file changed