Expose ARC++ version in metadata.json.

Expose ARC++ version and properly pass it from the master to slave
PFQ builders.

BUG=chromium:587927
TEST=cbuildbot_unittest
TEST=cbuildbot --local -p 'chromiumos/chromite' master-android-pfq
TEST=cbuildbot -p 'chromiumos/chromite' --buildbot --debug --nobootstrap --noreexec --buildroot /source3/buildbot-buildroot master-android-pfq

Change-Id: I86af19e766ad2044334fc837613eaa283e5838b2
Reviewed-on: https://chromium-review.googlesource.com/328847
Commit-Ready: David Riley <davidriley@chromium.org>
Tested-by: David Riley <davidriley@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
12 files changed