Move add/remove fixed ip action to servers_client

Add/remove fixed ips are server action and currently in
interface_client. As all other servers actions are in servers_client
so these two methods also should be in servers_client instead of
interface_client.

This commit moves add/remove fixed ips methods to servers_client.

Partially implements blueprint consistent-service-method-names

Change-Id: Idacc612bfed3d5a4abd58c8a987f68675b948f86
3 files changed