[OE-core] broken sstate archives

[André Draszik]

As a follow-up and as a reference for the future - having done countless
builds I am confident enough that a kernel update solved the problem:
- linux (Debian 9) versions 4.9.110-3+deb9u6 and 4.9.110-3+deb9u5 both
  exhibit the problem
- 4.18.6-1~bpo9+1 doesn't

Something must have gone into the btrfs driver to fix the issue. I didn't
really spend the time to try and find the relevant commit.

For reference, I am also sending my hackish patch to poky to detect
the error case early, which (tries) to detect the broken archive, and
simply runs tar again.

Thanks Richard for all your inputs.

Cheers,
Andre'