ctdb-scripts: Fix CTDB_DBDIR=tmpfs support

ctdb-scripts: Fix CTDB_DBDIR=tmpfs support

Various scripts (including debug_locks.sh, 00.ctdb, 05.system) need
CTDB_DBDIR to point to the right place... but it doesn't.

Move the rewriting of CTDB_DBDIR to loadconfig() so that it happens
for all scripts.  Have this code set internal variable
CTDB_DBDIR_TMPFS_OPTIONS so that ctdbd_wrapper can do the mount.

This loses the generality that was present in dbdir_tmpfs_start() but
it wasn't being used anyway.  If it is needed in the future then it
will be in the git history.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Wed Nov 18 11:51:54 CET 2015 on sn-devel-104