Refactor rest-client for using one class for both types 'json' and 'xml'

Current situation:
We have two rest-client classes, one for each container type - "json" and "xml".
Due to this structure, we need inherit for each service client different rest-clients,
it leads to write all service methods twice, even if it is the same.

The proposal is next:

Make one Rest-client class with conditions, where needed, for container type.
Dependencies for container type should be removed from __init__ method,
and placed to separate methods, which will read current value of TYPE option.

For example:

TYPE = 'json'

def _get_type(self):
    return self.TYPE

def get_headers(self):
    return {'Content-Type': 'application/%s' % self._get_type(),
                   'Accept': 'application/%s' % self._get_type()}

After that we can:
1) Create two service clients, where
2) json client inherits rest-client, and contains all service methods
3) xml client inherits json-client, redefines self.TYPE option and some methods, that are not similar.

In perfect case, we should have only several redefined methods, that decodes (parses) output and encodes request.

Finally, we can remove a lot of duplicated methods for each pair of service clients.