getVarFlags returns a dict and there is therefore no sort order. This
means the order of the X_VARDEPS_X variables can change and hence the
task checksums can change. This can lead to rebuilds of any parts of
the system using update-alternatives and their dependees. This is a
particular issue under python v3.
Add in a sort to make the order of the variables deterministic.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
