improve salt-run salt.cmd test

[Ch3LL]

What does this PR do?

improves the salt-run salt.cmd test. There was an issue on 2016.11.2 where out was returning:

'out': ['Exception occurred in runner salt.cmd:                                           
         Traceback (most recent call last):', '  File                                                                  
         "/home/ch3ll/git/salt/salt/client/mixins.py", line 397, in _low', "                                           
         if 'data' in data['return']:", "TypeError: argument of type 'bool' is                                         
         not iterable"]}

See issue #38638
This pr improves the test to make sure we catch this.

Tests written?

Yes