Add test for no-encoding-in-empty-file (W9905)

See
https://github.com/saltstack/salt-testing/pull/4#issuecomment-24727655
for discussion.
Don't know what I was thinking. Struck me when I was driving the car. :)
Merge pull request #6 from holmboe/develop

Add test for no-encoding-in-empty-file (W9905)