ctdb-eventscripts: Don't check if $iface is empty

ctdb-eventscripts: Don't check if $iface is empty

This is the loop variable.  It can't be empty, especially given the
way the list is built.  This must have survived from an earlier
version of the script.

Given that there are whitespace changes associated with the above,
clean-up the "virtio_net" avoidance check so that it reads less like
line-noise.

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