ctdb-tests: Correctly cascade test failures from the end of pipes

ctdb-tests: Correctly cascade test failures from the end of pipes

Some eventscript unit test failures get lost because _passed=false is
set in the tail of a pipe.  Add a new function test_fail() and call it
when necessary to ensure the value of _passed is set correctly.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Pair-programmed-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Autobuild-User(master): Martin Schwenke <martins@samba.org>
Autobuild-Date(master): Thu Mar  5 07:16:54 CET 2015 on sn-devel-104