ci-yadp-builder jobs: switch to using python3 version

After syncing up the yadp_builder.py from the
ci-yadp-builder repo, we should use it instead of
the yadp_builder_v2.py script (which is python2).

We should also call python3 explicitly instead of
relying on the system symlink to be present.

Signed-off-by: Kelley Spoon <kelley.spoon@linaro.org>
Change-Id: I244be8df7ed0149dc96e2c833bf2af37a2fb0eb7
2 files changed