Change check_mode() for AIX to NotImplemented

This is fix for #277.

You should set UNIX command to return the ocatal file mode, should not check the result here.
Rmoeve test of be_mod for AIX
Merge pull request #278 from serverspec/fix-aix

Change check_mode() for AIX to NotImplemented
Modify Gemfile to include Gemfile.local if it exists