Fix kwargs for FloatingIPPortAlreadyAssociated.

Updates the NVP plugin to use the correct kwargs when raising
l3.FloatingIPPortAlreadyAssociated.

Fixes LP Bug #1159922.

Change-Id: If89feea5e40976ccb4286f96f5348c54f84950ce
Merge "Fix kwargs for FloatingIPPortAlreadyAssociated."