brought up on IRC by @scn

It is only really needed for one last use case.

Inform users when the parameter we try to change depends on another
parameter.

This is not meant to be merged as-is, we could have a new VSB function
to trim the end of the string if it matches the one passed as the second
argument. In this case, we would trim the trailing newline only of the
CLI response didn't overflow in the first place, adding the extra
information on the same line. Alternatively we could also simply add the
explanation for the dynamic bounds on the next line.

Feedback welcome.

Fixes #3098

req->err_code and req->err_reason are set when going to synthetic
handling. From there the resp.reason HTTP field is set from
req->err_reason if set, or the generic code based on req->err_code is used
if it was NULL. This patch clears these members so that a value from the
handling of a previous request doesn't linger.

Fixes: VSV00004

This de-duplicates logic between the two hashing directors, and in
the case of vmod-shard adds a missing check for empty components in
the strands that should be skipped.

This breaks the hashing of the hash director, but unlike the shard
director it offers no stability and results may vary depending on the
health of individual clusters. For this reason only d00003.vtc needed
a bit of reshuffling.

I was in the neighborhood...

This reverts commit 6233b088.

Conflicts:
	bin/varnishd/cache/cache_req.c

The conflict was introduced with the handling of h2 stream 0 pseudo
request: 51127b46. This fixes a
regression where timeout_idle could be circumvented by a periodic
CRLF, except that it has no real consequence like holding onto a
worker thread thanks to timeout_linger kicking in as expected.

In addition to reverting the change, test coverage is added.

This reverts commit 762fda9a.

Failure to read the right number of bytes (typically due to remote HUP)
would log "straight insufficient bytes", which is the same as we log for
C-L based fetches. Change this to "chunked insufficient bytes". (Assuming
this was a copy-paste error).

Ref #3088

apparently the additional argument was just silently tolerated by
varnishtest

Tests #3088

Using vut->last_sighup was not adequate, because the VUT_Main loop might
have terminated for some other signal or because of EOF.

On the other hand, we do not want to end the curses loop just because
the VUT_Main loop has ended in order to continue to display the last
state (and maybe the EOF in the top right corner).

So while I see that checking just one flag has some beauty to it, I do
think that directly checking the signal counters is both simple and
robust.

Fixes #3088 for varnishtop and varnishhist

Fixes #3088 for varnishstat

note that besides handling SIGHUP, this also adds handling of SIGTERM
and SIGINT, which were also missing.

Refs a791188e

backend None does not actually create a backend, so tests which require
one need to use the bad_ip method.

... for those cases which can easily be changed (most of them).

This avoids issues with failing tests when bad_ip is actually reachable
via tcp on the respective port, as seen for example with b00068.vtc