Make sharness tests' output helpful when verbose.
This means cating certain files, or running diagnostic
commands. I used a construction like:

    test_expect_success ".go-ipfs/ has been created" '
      test -d ".go-ipfs" &&
      test -f ".go-ipfs/config" &&
      test -d ".go-ipfs/datastore" ||
      fsh ls -al .go-ipfs
    '

The `|| ...` is a diagnostic run when the preceding command
fails. `fsh` is a trivial script that echoes the args, runs
the cmd, and then also fails, making sure the test case fails.
(wouldnt want the diagnostic accidentally returning true and
making it _seem_ like the test case succeeded).