Initialize message loop in fuzzers am: dc26856986 am: 51760555f5

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

Change-Id: If379fa90e95d684b4c50be2e5924d77bf6dcf797
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>