Respect threading requirement of LifeCycle#addObserver/removeObserver am: f2e4fe45f5

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Virtualization/+/3538988

Change-Id: Ibc435d4b17628264a95cbc4da1cc8c4c4ffe971d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>