Don't return `None` in `salt.modules.dockerio.__virtual__()`.
The test needs to be executed as root to pass.
`os.getcwd()` might thrown an `OSError` if it was deleted or moved.

Let's not fail because of that.
Don't return `None` in `salt.states.dockerio.__virtual__()`.
Merge pull request #7882 from s0undt3ch/develop

Don't return `None` in `salt.modules.dockerio.__virtual__()`.