virttest.staging.service: Revert commit 69ac938

Turns out that change was made with little thought
with regards to the users of the code that already
existed.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest.nfs: Revert commit d2c21517

Make the nfs module use the service API previous to the
change made on 69ac938d.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest/nfs_unittest.py: Fix staging imports

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest.nfs: Fix imports to make unittest pass

In fact, previous fixes that make nfs to use the
staging library needed some tweaking to match
expectations.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>