The helpers for starting/stopping qemu-nbd in 058 will be useful in
other test cases, so move them into a common.nbd file.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>
Message-Id: <20181116155325.22428-4-berrange@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
[eblake: fix shell quoting]
Signed-off-by: NEric Blake <eblake@redhat.com>