Adds hacking check for api_version decorator

Because of the implementation of this decorator and the controller's metaclass,
the api_version decorator must be the outermost (ie first) decorator wherever
it is used. This patch adds a hacking check to ensure that this is the case.

This decorator is intended to be used on multiple methods with the same name
which offends F811, so '#noqa' is needed too. This will be fixed in a separate
patch.

Bad:
    @some_decorator # noqa  <-- '# noqa' to avoid F811
    @api_version("2.5")     <-- Error, needs to be the first decorator
    def my_api_method...

Good:
    @api_version("2.5") # noqa   <-- this line still needs '# noqa' for F811
    @some_decorator
    def my_api_method...

Change-Id: I579c0061f03d788c477c5424d4d00ec7a6e721e1
Merge "Adds hacking check for api_version decorator"