[platform] Move the stateful update from wget to curl

wget is removed from the rootfs crbug.com/781538 change the
stateful update to use curl rather than wget

TEST=ran unittests, will run trybot job before submit.

Change-Id: I0afc1b3e3f9520cc20f8ff65d38712b4957e010b
Reviewed-on: https://chromium-review.googlesource.com/773114
Commit-Ready: Keith Haddow <haddowk@chromium.org>
Tested-by: Keith Haddow <haddowk@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed