* Pass condition variable for client_state
* Notify all cond waiters when changing the transcation status to
aborted
* Wait for aborting transaction state aborted in before_command
Depending on the DBMS client session allocation strategy the
client id may or may not be available when the client_session
is constructed, therefore there should be a method to assign
an id after construction. Close/cleanup methods were added to
clean up open transactions appropriately.
