Enabled when using varnishtest -L.

(at leat on solaris) strerror() itself may fail for an out-of-memory
condition (because the localization code contains memory
allocations). In order to handle this situation, we need to save the
original errno because strerror() may also set errno.

This issue exists in many more places all over the code, but in the
pool_breed case we likely failed pthread_create for an out-of-memory
condition, and in the panic handler we want to make sure that we
trip no follow-up panic under any circumstances.

In general, while fixing all strerror() calls would unnecessarily
complicate the code, doing so should be justified for these cases.

Fixes #2815

the priv id is basically equivalent to the head (struct vrt_privs),
and a vrt privs list thus can not contain privs with another id.

So we could also retire the id member of struct vrt_priv...

we could also retire the vcl member of struct vrt_priv, but it could
be useful for debugging.

completely irrelevant historical note:

IIUC, ~20+ years ago, "slowlaris" was referring to Solaris being
percieved as "much slower than linux" (which was partly true, but
also related to the fact that linux had less mp support at the time)

Tests #2809

Fixes: 	#2809

Always make "* top %f TEST ${test} starting" the first message.

Tag vtest and varnishtest message with "VTEST" instead of "TEST"

The vmod name got lost in e7c04974

example before/after diff:

- new xshard_param = shard_param()
+ new xshard_param = directors.shard_param()

... after feedback from @slimhazard aka Geoff

Also quote \v as \v

... introduced with 8c113ff6

Here it seems the intention was to make sure that the access to the
parameter happens uncached, but even then it would not have helped.

Reviews appreciated.

I will most likely continue applying these changes in smaller chunks
because a) this kind of work is boring and b) in the hope that smaller
chunks will get reviewed better.

we INIT_OBJ the v1l, which includes a memset(0)