'Creates a consistencygroup from source.
:param context: the context of the caller.
:param group: the dictionary of the consistency group to be created.
:param volumes: a list of volume dictionaries in the group.
:param cgsnapshot: the dictionary of the cgsnapshot as source.
:param snapshots: a list of snapshot dictionaries in the cgsnapshot.
:param source_cg: the dictionary of a consistency group as source.
:param source_vols: a list of volume dictionaries in the source_cg.
:returns: model_update, volumes_model_update
The source can be cgsnapshot or a source cg.
param volumes is retrieved directly from the db. It is a list of
cinder.db.sqlalchemy.models.Volume to be precise. It cannot be
assigned to volumes_model_update. volumes_model_update is a list of
dictionaries. It has to be built by the driver. An entry will be
in this format: {\'id\': xxx, \'status\': xxx, ......}. model_update
will be in this format: {\'status\': xxx, ......}.
To be consistent with other volume operations, the manager will
assume the operation is successful if no exception is thrown by
the driver. For a successful operation, the driver can either build
the model_update and volumes_model_update and return them or
return None, None.'

def create_consistencygroup_from_src(self, context, group, volumes, cgsnapshot=None, snapshots=None, source_cg=None, source_vols=None):

    raise NotImplementedError()
