Moving ElasticSearch client into a plugin

Change-Id: I560d13a1fd83bfc149aa2f6053e0e4ca1fc308c4
Moving unittest2 into conditional requires

Unittest2 is only needed for py26 and under. As we want to eventually
be able to make OpenCAFE Python 3 compatible, we need to keep back-
compatiblity requirements on a conditional level.

Change-Id: Id7fc4ede4c1aef84759e72be0fac28c86b1a09bc