Fix delimiter on _check_compound_minions

Refs commits from #13716

Using compound matchers doesn't work since the addition of the custom delimiter with 9695c6e212d9873da33e7afa81a54fba3460f74e

Hopefully I'll have a setup of the test suite working with Docker, in order to add the compound matchers unit test.
Meanwhile, it can be tested with
```
[vagrant@salt ~]$ sudo salt -C 'G@foo:bar' test.ping
No minions matched the target. No command was sent, no jid was assigned.

[vagrant@salt ~]$ sudo tail /var/log/salt/master
  File "/usr/lib/python2.6/site-packages/salt/utils/minions.py", line 339, in _check_compound_minions
    results.append(str(set(matcher('@'.join(comps[1:])))))
TypeError: _check_grain_minions() takes exactly 3 arguments (2 given)
2014-09-18 02:49:38,032 [salt.utils.minions                         ][ERROR   ] Failed matching available minions with compound pattern: G@foo:bar
Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/salt/utils/minions.py", line 463, in check_minions
    minions = check_func(expr)
  File "/usr/lib/python2.6/site-packages/salt/utils/minions.py", line 339, in _check_compound_minions
    results.append(str(set(matcher('@'.join(comps[1:])))))
TypeError: _check_grain_minions() takes exactly 3 arguments (2 given)
```