[OE-core] [PATCH v4 2/2] selftest/wic: Add tests for --exclude-dir option.

[Kristian Amlie]

Rebased and reran tests. Changes since last patchset:

- Because of recipe specific sysroots we now need to import the PATH
  used by wic-tools into the test in order to use its tools.

- Add specific '-o' parameter while testing wic so that we write into
  resultdir.

- Several unrelated changes to poky now means that we need to use an
  absolute path for new_rootfs in the rootfs.py implementation. This
  would have been a good idea from the start anyway.

I hope there are no more outstanding issues with this patchset.

-- 
Kristian