OSDMonitor: add debug_fake_ec_pool

This flag will cause ReplicatedPG to act as though the
pool were actually an EC pool in that operations will
be restricted to operations which can be locally rolled
back thereby allowing us to test the ReplicatedPG local
log rollback mechanisms independent of EC.  It will also
cause ReplicatedPG to use the async read mechanism on
the PGBackend implementation once it is implemented.

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGBackend: add PGTransaction

Signed-off-by: Samuel Just <sam.just@inktank.com>
hobject_t/ReplicatedPG: tempness is now an hobject thing

PGBackend implmentations will have complete control over the temp
collection.  Rather than specifying the collection when sending
ops into the PGBackend, hobjects themselves will be temp or not.

Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedBackend: implement RPGTransaction

RPGTransaction is essentially a wrapped ObjectStore::Transaction.
The coll_t argument is elided, tempness is instead encoded in the
hobject.  RPGTransaction tracks which temp objects are created and
cleared so we can update the ReplicatedBackend tracking and possibly
create the temp collection as needed.

Signed-off-by: Samuel Just <sam.just@inktank.com>
PG/ReplicatedPG: move snap map management into append_log

Both the replica and the primary should use the same append_log
mechanism to update the snap map.

Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: split out op_applied_replica

Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: factor out should_send_op

Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedBackend.h: don't need to be active for pushes

Signed-off-by: Samuel Just <sam.just@inktank.com>
ObjectStore: improve name of the queue_transaction which cleans up the transaction

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGBackend: allow queue_transaction to specify an op

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd/: move client op handling into ReplicatedBackend

Signed-off-by: Samuel Just <sam.just@inktank.com>
hobject: admit that gen_t is actually version_t

Signed-off-by: Samuel Just <sam.just@inktank.com>
PGBackend: add interfaces for stashing removed objects

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd_types: pg_log_t record oldest version to which we can rollback

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd_types: hook ObjectModDesc into pg_log_entry_t

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd/: introduce xattr caching for ec pools

Signed-off-by: Samuel Just <sam.just@inktank.com>