Novaclient flavors.create needs cleanup

The conversion from integer-only required flavor ids in novaclient to allowing string ids and autogenerated ids needs some cleanup. REferring to the code here:

https://github.com/openstack/python-novaclient/blob/master/novaclient/v1_1/flavors.py#L107

  1. The docstring still refers to the id as a required integer.

  2. The flavor id argument, given it's position, could have been converted into a kwarg with a value of None with no alteration to the method signature. This would have eliminated the need for the "auto" special-cased name.

  3. The current implementation means that you can't create a flavor named "auto". While this isn't a huge issue, it is still an unnecessary artificial restriction on the possible set.