Ignore lifecycle events for non-existent instances

Since event delivery is asynchronous, there's an inherent yet benign race in the
event handler querying the database for a deleted instance.

Fixes bug #1180501.

Change-Id: I8e478fb13bedfc86730018ba849ecc71d4286f0d
Merge "Ignore lifecycle events for non-existent instances"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp