classes/populate_sdk_ext: check that extensible SDK prepared correctly
After the change to use --setscene-only when running bitbake to prepare
the SDK at the end of installation, add a check that the SDK got
prepared correctly by doing a dry-run and looking at the output for any
real tasks that we don't expect. In order to make this easier, the
preparation shell script was rewritten in python.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
