Add a --node-ip argument so that one can specify which ip address a

Add a --node-ip argument so that one can specify which ip address a
specific instance of ctdbd should bind to. This helps when running a
"virtual" cluster on a single machine where all instcances bind to
different alias interfaces.

If --node-ip is specified, then we will only try to bind to this ip
address only. Othervise we fall back to the original method trying the
ip addresses in /etc/ctdb/nodes one by one until we find one we can bind
to.

No variable in /etc/sysconfig/ctdb added since this parameter only makes
sense in a virtual test/debug cluster.

(This used to be ctdb commit d96cb02c2c24f9eabbc53d3d38e90dea49cff3e0)