Fixes for the NFS role

This adds most of the functionality that we require.

The template for the exports still needs to be changed so that it is
more secure by default. It is currently using the no_root_squash so that
the PAM mkhomedir functionality works as expected.
Fix Nginx vhost template

Check if upstream is defined first.

Some static servers will not have upstream servers.
Remove NFS exports from group_vars/all

NFS will not be used on all servers so remove from group_vars/all.