Combined old and new functionality of elliptics.Node.add_remote. Added tests for elliptics.Node

 Now remote can be added by follow ways:
  * node.add_remote("host:port:family")
  * node.add_remote("host", port)
  * node.add_remote("host", port, family)
  * node.add_remote(elliptics.Address)
  * node.add_remote(["host:port:family", elliptics.Address])

Pytests: added tests for elliptics.Node: tests adding remotes in different manners.