Inspired by: #2488

This needs a separate job. Also fix previous commit.

@bsdphk to be discussed / replaced

entire process group on timeout.

This still leaves the case where the process group leader exits
without a timeout but some of its subprocesses failed to stop.

Relevant to: #2469

unused since 992d5250

Please do not assume this to be complete since 5.2 release

Please do not even assume my XXXes to be completely referencing the missing bits.

Waving @slimhazard / Geoff from the ICE train and Berlin U-Bahn/S-Bahn

I wonder if maybe varnishd start should not return before accepting?

Ref: 6cb21b47
     #2382

Afterthought on #2405:

The usage pattern we want to get to is (pseudo vcl, don't take
the syntax for granted)

	sub vcl_whatever_client_sub {
		std.rollback(req);
		set req.<whatever>;
		...
		return (restart);
	}

The hash and storage controls should be no exception

Rewrite the CLI command acceptance to not use the VLU functions,
but a small state machine.

Unauthenticated CLI sessions have a hard limit of 80 char cmds
and cannot use the "<< nonce" construct.

... not for any vsm change.

Fixes #2430

Merges #2447

Fixes #2405 for restarts
Merges #2447

remaining TODOs (but not the scope of this ticket):

* Keep bereq attributes for bereq
* improved rollback

I see absolutely no reason why we shouldn't allow read access outside
vcl_recv

Merges #2447