For inexplicable reasons the NFS volume driver was put into a
different file than all the other libvirt volume driver impls.
The NFS code isn't so large & complex that it needs to be in
a different place than everything else. Move the code into
the main volume.py file.
To avoid breaking existing deployments, the original class
has to be a trivial subclass of the new module. Any use of it
will trigger a deprecation warning. This allows time for users
to update their 'libvirt_volume_drivers' config (in the unlikely
event they have altered from the default setting).
Change-Id: I26d957e4ee33938b45dc1cad0fe32a2968520a4a
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>