Using positions in lists for flags is an odd choice and makes the code
hard to maintain. Maintaining a list is slow since list searches are
slow (watch bitbake -n slow massively with it) but we can use a set()
instead.
This patch uses python sets to maintain the lists of tasks in each state
and this prepares for changing the task IDs from being integers.
(Bitbake rev: 8c1ed57f6ea475b714eca6673b48e8e5f5f0f9c3)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>