'Check to see if an initiator group already exists.
NOTE:  An initiator/wwn can only belong to one initiator group.
If we were to attempt to create one with an initiator/wwn that is
already belonging to another initiator group, it would fail.
:param serial_number: the array serial number
:param initiator_names: the list of initiator names
:returns: initiator group name -- string or None'

def _find_initiator_group(self, serial_number, initiator_names):

    ig_name = None
    init_list = self.rest.get_in_use_initiator_list_from_array(serial_number)
    for initiator in initiator_names:
        found_init = [init for init in init_list if (initiator in init)]
        if found_init:
            ig_name = self.rest.get_initiator_group_from_initiator(serial_number, found_init[0])
            break
    return ig_name
