qubes/app: do not enable domain events when loading XML
qubes/app: do not enable domain events when loading XML

Event should be enabled only after all the domains are loaded (and
domain-load event if fired).

QubesOS/qubes-issues#1816

woju/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin