nfs-ha-cluster-ubuntu does nto work on Ubuntu 18.04

### Issue Details
* deploying nfs-ha-cluster-ubuntu using ubuntu 18.04 does not work, the storage is created and mirrord, but running ``showmount -e {node balancer ip}`` fails.

If I deploy a cluster with ubuntu 16.04 it works fine.

### Repro steps (*if necessary, delete otherwise*)
1. Use "deploy to azure" button [here](https://azure.microsoft.com/en-us/resources/templates/nfs-ha-cluster-ubuntu/)
2. change in settings os type from ``{"offer":"UbuntuServer","publisher":"Canonical","sku":"16.04-LTS","version":"latest"}`` to ``{"offer":"UbuntuServer","publisher":"Canonical","sku":"18.04-LTS","version":"latest"}``
3. deploy

expected:
nfs mount should work

result:
nfs server is not available and hags

Attaching storage configuration (removed public key, I can ssh to the machines without problem).

Start with the nfs-ha-cluster-ubuntu template linked in the issue and reproduce the deployment using the Azure Deploy button with Ubuntu 18.04, then compare it with Ubuntu 16.04. Run `showmount -e {node balancer ip}` and verify that the NFS export is available and can be mounted on the 18.04 cluster.

Written by the indexing model from the issue text.