Refactor and add tests for db_replicator

* Create class for testing _repl_to_not and replicate_object fuctions to
  prevent duplication code by adding all preparation into setUp function.
* Move existed test function which testin _repl_to_not and
  replicate_object into created classes.
* Add tests for replicate_object and _repl_to_node functions.

Change-Id: I75ac7c6f0230e71bfb24328e44c33734b520b4cd
Merge "Refactor and add tests for db_replicator"