cbuildbot: call new chromite pushimage

Switch from the crostools version to the new chromite python one.

While we're here, drop the "branch" argument to PushImages.  The old
bash script accepted it but never actually used it.  The new python
script doesn't bother accepting it.

We also lighten up the unittests on the cbuildbot side of things.
The pushimage code itself now has a lot of unittests, and the API
is just a pass thru, so no need to stress it here.

BUG=chromium:327571
TEST=`./buildbot/run_tests` passes
TEST=`cbuildbot link-firmware` passes
TEST=`cbuildbot arm-generic-full` passes

Change-Id: I5004096dfc66bb486593356350c2838d064a18c2
Reviewed-on: https://chromium-review.googlesource.com/182402
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
3 files changed