bitbake: runqueue: Improve multiconfig deferred task issues

The previous patches have exposed new issues with this code path,
the issues being around what should happen when the hash of a task
changes and the task is or is not on the deferred task list.

Rather than rebuilding the deferred task list during each rehash
event, build it once at the start of a build. This avoids the problem
of tasks being added back after they have run and also avoids problems
of always ensuring the same task is deferred. It also allows the
'outrightfail' codepath to be handled separately as the conditions
are subtly differnt.

One significant win for the new approch is the build is not continually
printing out lists of deferred tasks, that list remains fairly static
from the start of the build. Logic is added in to ensure a rehashed
task with a hash matching other deferred tasks is deferred along with
them as a small optimization.

An interesting test case for this code was reported by Mark Hatle
with four multiconfigs, each the same apart from TMPDIR and running a
build of:

bitbake buildtools-tarball mc:{one,two,three,four}:core-image-minimal

which is interesting in that the build of buildtools partially overlaps
core-image-minimal and the build has a rehash event for qemuwrapper-cross
even without any external hash equivalence server or preexisting data.

(Bitbake rev: bb424e0a6d274d398f434f7df63951da9ce305b3)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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