Our %h formatter was broken and we did not notice due to coincidence of
two reasons:

Before 626ddb029256513b6de36d5e642299d6708d638d in varnish-cache,
varnishncsa did not output %h for our (ancient) test file because it
does not contain BackendStart records.

varnishevent did not output %h because it was using SLT_Backend, which
had been removed from varnish-cache for long.

Because both matched, we did not notice any issue.

It is only now due to the change from
626ddb029256513b6de36d5e642299d6708d638d that we noticed the issue.

So the fix is to take %h from SLT_BackendOpen and adjust all other test
details in this regard.

The fix in varnish triggered the ncsa.sh test failing because
varnishevent would also not format %h correctly: SLT_Backend had been
retired for long, but we still took %h from it.