search for: test_nbdkit_template

To avoid bitrot, any new feature needs testsuite coverage ;) Still to come: once I get my work on parallel nbd finished, I will add a test-parallel-nbd.sh that closely mirrors what my other series added in test-parallel-file.sh. If desired, it might be a fun exercise to tweak test-nbd into using a for-loop of user-controlled depth for how deep you want to nest the forwarding tree, to see where