runqueue: Fix data being written into siginfo/sigdata files

The way hash_deps was being generated was different to the way siggen generated
the data internally which lead to seemingly different sigdata/siginfo files
for the same checksum. The -S output correct but the files written during
builds contained superflous data which would look like a difference.

This patch removes the badly duplicated data and uses it from the source
which ensures its consistent.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
siggen: When printing signatures recursively, limit the output

Currently the code prints all differences. If the task dependencies have changed hash,
we recurse into those and print those differences as well. This leads to a lot
of output. The reality is if the parents changed signature, we might as well just
say that and recurse with no other output since we're much more interested in how
the parents changed in nearly all cases. The changes in the parent are probably
the same ones we'd have printed at each level anyway.

By doing this we focus the output more carefully on the thing the user wants/needs
to see.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
runqueue: Further extend bitbake -S output to view signature differences

Based upon the list of difference starting points, we can use the siggen.find_siginfo()
function call and the difference printing code to provide a list of differences
between the current build target and whatever can be obtained from the sstate cache.

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