fixup "PG: switch the start_recovery_ops interface to specify work to do as a param"

Pass out params as pointers instead of references

Signed-off-by: Greg Farnum <greg@inktank.com>
squash "ReplicatedPG: implement the RWTracker mechanisms for backfill read locking"

Instead of requeueing in the RWTracker, take a bool out param indicating
that the caller should requeue recovery work.
fixup "ReplicatedPG: RWTracker: always set backfill_waiting_on_read=true"

We can't assert !backfill_waiting_on_read because we might be the
second attempt to grab the lock, after having it be previously contended.
D'oh.