Register service with servicemanager and name the context.

avc: denied { call } for scontext=u:r:update_engine:s0 tcontext=u:r:servicemanager:s0 tclass=binder
avc: denied { add } for service=android.os.IUpdateEngine scontext=u:r:update_engine:s0 tcontext=u:object_r:update_engine_service:s0 tclass=service_manager

Also allow priv_app to communicate with update_engine.

avc: denied { find } for service=android.os.IUpdateEngine scontext=u:r:priv_app:s0:c512,c768 tcontext=u:object_r:update_engine_service:s0 tclass=service_manager
avc: denied { call } for scontext=u:r:priv_app:s0:c512,c768 tcontext=u:r:update_engine:s0 tclass=binder
avc: denied { call } for scontext=u:r:update_engine:s0 tcontext=u:r:priv_app:s0 tclass=binder

Change-Id: Ib4498717c1a72f5faab5ea04c636924ee4eb412c