Move floating IP and floating IP pools functionality from a base compute
OpenStack class into a separate mixin classes and update providers which offer
this functionality to also inherit from those mixin classes.

Also add new OpenStack_1_1BaseNodeDriver which only contains common
functionality and should only be inherited from and never instantiated directly.
OpenStack_1_1_NodeDriver will inherit from Base class and all the extension
mixin classes and still function as previously.