SERVER-8375 sync from primary on clock skew

testing this was difficult (as we couldn't manage to simulate a cycle)
what I eneded up doing was:
    1. added a fail point to oplog such that when the fail point is active the new code will be hit
    2. altered sync_passive2.js (because it had chaining in it) to do the chaining portion twice with the failpoint active the second time to make sure the new code caused us to sync from the primary again
    3. https://gist.github.com/dannenberg/dcda9353b637edda6a16 for the full diff