ctdb-scripts: Tunables are now loaded from ctdb.tunables

ctdb-scripts: Tunables are now loaded from ctdb.tunables

Using CTDB_SET_TunableVariables in the main configuration file is no
longer supported.

The only subtlety is an unexpected order change in one of the unit
test results.  This is because the old implementation implicitly
sorted the tunable variables via the set command.

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