eventscripts: Rewrite the smb.conf cache file handling

eventscripts: Rewrite the smb.conf cache file handling

The background update is never guaranteed to complete before the cache
is used, so don't bother trying it at the beginning.  Instead, put a
timeout on a foreground update.

If the foreground update fails:

* If there's no available cache file then die.

* If there is a previous cache file then use it and log a warning.

* Do a background update at the end of the monitor event.

Also remove commas in the "smb ports" list before use, since (newer?)
testparm seem to insert commas into the default value.  Update the
associated test to add a comma.

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