Fix rendering of FixedIpNotFoundForNetworkHost

Fixes bug 1104000

With https://review.openstack.org/18319 a small bug was introduced. The
exception FixedIpNotFoundForNetworkHost is expecting network_id
parameter, and the change modified that parameter to network_uuid. This
patch fixes this problem at the raise point.

Change-Id: Idc0fa7fcba9ad37b73183f8811376c6c8adada68