novaclient supports v4-fixed-ip and v6-fixed-ip as aliases for fixed_ip.
As shade used to use novaclient and passed this content through the
switch to REST resulted in a behavior regression for shade users. That's
bad, mmkay?
Add in support for the same aliases to create_server, so that users
upgrading to newer shade are hosed.
Closes-Bug: #1798489
Change-Id: I55bc88e9b2cfa5ad1b6a27640db11bc848584c21