osd/PG: Add two new mClock implementations of the PG sharded operator queue

osd/PG: Add two new mClock implementations of the PG sharded operator queue

Create an mClock priority queue, which can in turn be used for two new
implementations of the PG shards operator queue. The first
(mClockOpClassQueue) prioritizes operations based on which class they
belong to (recovery, scrub, snaptrim, client op, osd subop). The
second (mClockClientQueue) also incorporates the client identifier, in
order to promote fairness between clients.

In addition, also remove OpQueue's remove_by_filter and all possible
associated subclass implementations and tests.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>