ctdb-ipalloc: Fix buggy short-circuit when no IPs are available

ctdb-ipalloc: Fix buggy short-circuit when no IPs are available

At the moment IP is short-circuited when there are no available IP
addresses.  However, if some IP addresses are already allocated then
"no available IP addresses" means that all the addresses should
(probably) be released.  The current short-circuit means that no
already hosted IP addresses will be released.

The short-circuit exists to avoid lots of messages saying that all IP
addresses can not be assigned at startup time.  So, add a check to
ipalloc_can_host_ips() so that it succeeds if IP addresses are already
allocated to nodes.

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