ctdb-utils: Fix CID 1125558 (Unchecked return value from library)

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

Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Wed Jun  5 12:09:56 UTC 2019 on sn-devel-184
