ctdb-scripts: Change statd-callout to be more scalable

ctdb-scripts: Change statd-callout to be more scalable

Updating ctdb.tdb on each add-client, del-client and each delete
during notify was too ambitious.  Persistent transactions do not
perform well enough to do this.

Revert to having add-client and del-client create touch files.  Each
monitor event calls "statd-callout update" to convert touch files into
ctdb.tdb records.

Update testcases to do the "update" and add an extra test.

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