Fix disableStartStopDaemon() if /sbin/initctl is not present
Add changelog entry for Patryk Ściborek's fix
xen-delete-image: Proper error message if --test is not used with --dir

Also abort earlier in this case.

Closes: #704878
xen-delete-image: Exit with return code != 0 in all error cases
Fix cases where maxmem is not defined

(which is fine)
Refactoring: xt-create-xen-config: Use s/// to strip trailing MB size suffixes