Streaming rollback for total order BF abort used regular
BF abort codepath, which was not correct because the streaming
rollback must fully complete before total order operation executes.
Fixed this by adjusting bf_aborted_in_total_order_
before streaming_rollback() gets called.
Storing information that background rollbacker in ongoing in client state has_rollback_
This can be used for detecting if there is ongoing background rollback,
and client should keep waiting in before_command() entry to avoid conflicts
in accessing client state during background rollbacking.
transaction::bf_abort() is modified to set has_rollback_ flag when
backgroung rollbacking has been assigned for the client
sync_rollback_complete() method has been modified to reset the backround
rollbacker flag
