tests: fix a fix for too short delay in 201_shutdown_event_race test
tests: fix a fix for too short delay in 201_shutdown_event_race test

It's _domain_stopped_lock, not startup_lock.

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