vm: emit property-reset:stubdom_xid event on domain start/stop too
vm: emit property-reset:stubdom_xid event on domain start/stop too

Similart to property-reset:xid, emit property-reset:stubdom_xid when
domain is started/stopped. This allows client side of the Admin API
(qubes-core-admin-client) to invalidate the cache when necessary.

Found by audio tests: #352

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