mark testPushRetry as failing.  Remove commented code

https://github.com/couchbase/couchbase-lite-android/issues/398
Test the headers as part of mockSinglePull()

Hoping to remove TestHeaders

https://github.com/couchbase/couchbase-lite-android/issues/398
use stopReplication to stop replications

https://github.com/couchbase/couchbase-lite-android/issues/398