Check the passed regex against the available minions' public keys
        stored for authentication. This should return a set of ids which
        match the regex, this will then be used to parse the returns to
        make sure everyone has checked back in.

def check_minions(self,
                      expr,
                      tgt_type='glob',
                      delimiter=DEFAULT_TARGET_DELIM,
                      greedy=True):
        '''
        Check the passed regex against the available minions' public keys
        stored for authentication. This should return a set of ids which
        match the regex, this will then be used to parse the returns to
        make sure everyone has checked back in.
        '''

        try:
            if expr is None:
                expr = ''
            check_func = getattr(self, '_check_{0}_minions'.format(tgt_type), None)
            if tgt_type in ('grain',
                             'grain_pcre',
                             'pillar',
                             'pillar_pcre',
                             'pillar_exact',
                             'compound',
                             'compound_pillar_exact'):
                _res = check_func(expr, delimiter, greedy)
            else:
                _res = check_func(expr, greedy)
            _res['ssh_minions'] = False
            if self.opts.get('enable_ssh_minions', False) is True and isinstance('tgt', six.string_types):
                roster = salt.roster.Roster(self.opts, self.opts.get('roster', 'flat'))
                ssh_minions = roster.targets(expr, tgt_type)
                if ssh_minions:
                    _res['minions'].extend(ssh_minions)
                    _res['ssh_minions'] = True
        except Exception:
            log.exception(
                    'Failed matching available minions with %s pattern: %s',
                    tgt_type, expr)
            _res = {'minions': [], 'missing': []}
        return _res