'Creates a consistencygroup.
:param context: the context of the caller.
:param group: the dictionary of the consistency group to be created.
:returns: model_update
model_update will be in this format: {\'status\': xxx, ......}.
If the status in model_update is \'error\', the manager will throw
an exception and it will be caught in the try-except block in the
manager. If the driver throws an exception, the manager will also
catch it in the try-except block. The group status in the db will
be changed to \'error\'.
For a successful operation, the driver can either build the
model_update and return it or return None. The group status will
be set to \'available\'.'

def create_consistencygroup(self, context, group):

    raise NotImplementedError()
