os/bluestore: introduce multithireading sync for bluestore's repairer

os/bluestore: introduce multithireading sync for bluestore's repairer

In quick-fix mode bluestore uses 2 threads by default to perform the
repair. Due to lacking synchronization they might corrupt repair
transaction batch.

Fixes: https://tracker.ceph.com/issues/50017
Signed-off-by: Igor Fedotov <ifedotov@suse.com>
(cherry picked from commit 38c5b04235402a7908bc4713f617d767ca9fdc56)

 Conflicts:
	src/os/bluestore/BlueStore.cc - future stuff attempted to sneak
in
	src/os/bluestore/BlueStore.h - the same as above