OSD: Deleting transaction object right after applying transaction

OSD: Deleting transaction object right after applying transaction

Presently, the transaction object is been deleted by the Finisher
thread asynchronously. In heavy load scenario specially if we
unleash journal throttle more, we are seeing high memory usage by
the OSDs because of this. In this new scheme, with the help of
move semantics transaction objects will be deleted synchronously
from the filestore worker threads. We are seeing very much
controllable memory growth now as well as ~3 to 4% cpu usage
benefit because of some reduction of 'new' , 'delete' calls.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>