'Retrieve or create an initiator group.
:param serial_number: the array serial number
:param init_group_name: the name of the initiator group
:param connector: the connector object
:param extra_specs: the extra specifications
:returns: name of the initiator group -- string, msg'

def _get_or_create_initiator_group(self, serial_number, init_group_name, connector, extra_specs):

    msg = None
    initiator_names = self.find_initiator_names(connector)
    LOG.debug('The    initiator    name(s)    are:    %(initiatorNames)s.', {'initiatorNames': initiator_names})
    found_init_group = self._find_initiator_group(serial_number, initiator_names)
    if (found_init_group is None):
        found_init_group = self._create_initiator_group(serial_number, init_group_name, initiator_names, extra_specs)
        LOG.info('Created    new    initiator    group    name:    %(init_group_name)s.', {'init_group_name': init_group_name})
    else:
        LOG.info('Using    existing    initiator    group    name:    %(init_group_name)s.', {'init_group_name': found_init_group})
    if (found_init_group is None):
        msg = ('Cannot    get    or    create    initiator    group:    %(init_group_name)s.    ' % {'init_group_name': init_group_name})
        LOG.error(msg)
    return (found_init_group, msg)
