Re-factored cli options merging with the config into it's own mix-in. Refs #2563.

This will be useful in `salt-cloud` which copied this functionality over.
Update the remaining parsers to use `MergeConfigMixIn`. Refs #2563.
Merge pull request #3498 from s0undt3ch/develop

Re-factored cli options merging with the config into it's own mix-in. Refs #2563.