Delete instance metadata when delete VM

* like everything else instance metadata is just soft deleted.
* This doesn't soft delete instance_system_metadata (bug 1153827)

Fix bug 1092408

Change-Id: Iebc2c7e055a110e5067829569127a272a1a92a87
Merge "Delete instance metadata when delete VM"
Merge remote-tracking branch 'm_src_repo/master' into build-temp