Arcyd: fix reporting of failed repos on arcyd dash

Report a repo as failed from the reporeporter if there's a
traceback, fix the mismatch between status on arcyd dashboard and
per-repo dashboard.

Test Plan:
introduce deliberate exception in processrepo
$ ./testbed/arcyd/loop_test.sh
verify that status is reported correctly
$ ./precommit.sh
Arcyd: minor change to arcyd status 'schema'

Use a more explicit name for the per-repo status so it doesn't collide
with the arcyd-wide status.

Test Plan:
$ ./testbed/arcyd/loop_test.sh