When running with local daemons, provided there is more than 2 of

When running with local daemons, provided there is more than 2 of
them, randomly pick a single node that will not have any public IPs
assigned.  This will make life a bit more interesting and will
simulate what happens on real clusters with a management node.  Some
tests were disabling a node to implicitly trigger a ctdb restart - now
use an explicit restart of ctdb when it is required.
17_ctdb_config_delete_ip.sh now randomly chooses a public IP on any
node to disable - this works around a problem where the hardcoded node
might not have any public addresses.

Signed-off-by: Martin Schwenke <martin@meltin.net>
(This used to be ctdb commit 3d59783c0e9478f4766c380945d6200fc654f5d9)