Warn about wrong ID in arc download D8O88
Summary: It also disables arc download F7312-rainbow.
Test Plan:
arc download D8O88 arc download F7312-rainbow arc download F7312
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, epriestley
Differential Revision: https://secure.phabricator.com/D1768