powerofftestvms.sh needs to wait until test VM is off

[pcfe]

SOE-CI runs in quick succession with pipeline, poweroff = yes, the host may not be off yet when the 2nd run is active.

Make the script powerofftestvms.sh check every 15 seconds for 5 minutes after issuing the off command and only return when the 5 mins expired (exit 1) or when the test VM is reported as off. (can not cheat by force poweroff of the VM as in a run without re-install I want a clean shutdown