Revert "cooker: now that we use a Pool, raise the exceptions"

Reverting the pool changes, terminate does not work reliably on
bb.compat.Pool :(

This reverts commit 9ca8e513dc142dd7aefadeb6db2ccdb00f38b39f.
Revert "cooker: parse using bb.compat.Pool"

Reverting the pool changes, terminate does not work reliably on
bb.compat.Pool :(

[YOCTO #3978]

This reverts commit 8af519a49a3374bd9004864ef31ca8aa328e9f34.