ctdb-tests: Conditionally use temporary config file for local daemons

ctdb-tests: Conditionally use temporary config file for local daemons

If there's configuration in the environment then daemons_start()
should use a temporary configuration file with that appended.

This means that global overrides don't (harmlessly) build up in the
configuration file during each test and individual tests can override
configuration when calling daemons_start() directly.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12180

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