DO NOT MERGE Race condition in JobServiceContext

BUG: 23981171
JobServiceContext has a reference to the running job which
1) needs to be copied before providing access to outside callers
2) was not guarded by a lock in one case which might result in an NPE

Change-Id: I7eb04052f3fe63e7b386c564a6bdebf9144e976a
(cherry picked from commit 0cc7654e)