Dropping the use of 'AddFixedIp' server action entirely in favour of
creating an interface with a fixed IP using the 'os-interface' API. The
reason for doing this is because this mechanism allows us to request an
explicit fixed IP.
Adds back support for using the --fixed-ip-address argument for users
who use older nova-api versions.
Change-Id: Ieac4b0fbcb38fe7207eaaa6a79e0c6770ee11d80
e91844dd0e