ctdb-scripts: Split CTDB configuration loading

ctdb-scripts: Split CTDB configuration loading

loadconfig() currently tries to load the CTDB configuration and also
any system configuration relevant to the current (event) script.

Instead add a new function load_system_config() to load the
distribution-specific system configuration for a component.  Call this
directly in the rare scripts that need the system configuration.

Also call load_system_config when loading the CTDB configuration to
pull in anything from the CTDB system configuration.  This is partly
for backward compatibility but also to get options that can be used
anywhere.

loadconfig() no longer takes an argument.  It simply loads the CTDB
configuration.

Drop support for falling back to /etc/ctdb/sysconfig/ctdb (or
similar).  Surely there's nobody who uses that!

Also, drop the indirection where loadconfig() calls _loadconfig().
This was used years ago as a test hook and is no longer required.

Inexplicably, this change introduces a new shellcheck test failure, so
silence this.

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