Properly pass `__env__` to states.

* Add a test case to check for proper env selection when passing `?env=foo`. Refs #8196.
* Correctly trigger the issue reported on #8196.
* There won't be a Salt `0.20.x`.
* Log the env in use.
* Skip known state internal keys.
* Set the proper `__env__` as a function global when calling the state function. Fixes #8196.
* Accepting `__env__` as a keyword argument is no longer required or acceptable
* Deprecated `env` as a keyword argument since `__env__` is now available within the function's global scope.
* Updated test cases to include environment selection in states using `__env__`.