I am trying to live migrate my hosted engine between two hosts.  

Both hosts are now up.

The hosted engine exists on shared NFS storage mounted on both hypervisors.

Though when I tried to migrate the VM I am told that's not possible.

Could this be since I never defined migration network?  If so I tried doing that in the oVirt UI as described https://ovirt.org/documentation/admin-guide/chap-Logical_Networks/ though many of these options have changed.