When a before_* hook script returns 1, the calling action fails and reports an error code to Engine. The "message" field reported with the error code should include the stderr of the hook, so that it is easier to discern the cause of the error from Engine event log alone.
Verified in vdsm-4.17.19-0.el7ev.noarch used: vdsm-hook-httpsisoboot-4.17.20-0.el7ev.noarch - run VM from iso (https) with wrong address.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://rhn.redhat.com/errata/RHBA-2016-0362.html