Handle "rebooting" event generated by rhts-reboot

If a "rebooting" event is generated, do not set the task to done, if the
process exits for whatever reason.

Bug: 908354
Change-Id: Idc7b4e62f3a4e9ca88996033c9ac2eb9e7a2f4a7
Add before and conflicts on shutdown.target for beah systemd services
Release note for 0.7.6
Automatic commit of package [beah] release [0.7.6-1].