ctdb-tests: Shut down transaction_loop clients more cleanly

ctdb-tests: Shut down transaction_loop clients more cleanly

A transaction_loop client can exit with a transaction active when its
time limit expires.  This causes a recovery and causes problems with
the test cleanup, which detects unwanted recoveries and fails.

Set a flag when the time limit expires and exit cleanly before the
next transaction is started.

Pair-programmed-with: Amitay Isaacs <amitay@gmail.com>
Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>