[yocto] Invalidating tasks

[Anton Gerasimov]

Hi all,

I've got two tasks, `do_A` and `do_B` (they are really IMAGE_CMDs if
it's important). Now I want to introduce a third task,
`do_check_A_and_B`, that will test that `do_A` and `do_B` have produced
a correct result. If the test fails, I want to invalidate results of A
and B, so that they re-run next time I run `bitbake some-image`. Is it
possible? I've seen some "invalidate_task" functions in bb.siggen and in
bb.runqueue, but I'm not sure about how to use them in a recipe/bbclass.

Thanks,
Anton Gerasimov