ctdb-scripts: Allow load_script_options() to specify an event script

ctdb-scripts: Allow load_script_options() to specify an event script

This allows other scripts to use the given options for a particular
event script.  One interesting example is that the ctdb_natgw tool
should look for configuration in events.d/11.natgw.options.

In the future this will be something like
events/failover/11.natgw.options, so require the component to be
specified even though it isn't yet used.

Test support is also updated.

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