make change tracker delay configurable by tests

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

https://github.com/couchbase/couchbase-lite-android/issues/398
allow tests to change INBOX_CAPACITY

https://github.com/couchbase/couchbase-lite-android/issues/398
log the retry delay

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