Grep module does not support all the test cases

[gmiu]

We need to support also the case when a certain pattern must be contained by the output of __salt__[file.grep](). See an example from the old cis.py module:

ret = _grep('"/tmp"', '/etc/fstab')
    if 'nodev' in ret:
        CIS['Passed'].append(benchmark)
    else:
        CIS['Failed'].append(benchmark)
    return CIS