ctdb-scripts: Wait until IPv6 addresses are not "tentative"

ctdb-scripts: Wait until IPv6 addresses are not "tentative"

There are a few potential failure modes when adding an IPv6 address.
It takes a little while of duplicate address detection to complete, so
wait for a while.  After a timeout, also need to check to see if
duplicate address detection failed - if it did then actually drop the
IP address.

This really needs some careful thinking.  If CTDB disappears on a node
but the node's IP addresses are still on interfaces then the above
failure mode could cause the takeover nodes to become banned.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
(cherry picked from commit d0b2375c3d754da3cd68e34617ab3edd36e9317b)