Initialize message loop in fuzzers am: dc26856986

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2626919

Change-Id: Id8e28598e01eb2a97f7d235f0d950266da0b909c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>