arcyd-tester: refactor, split adding repos

Split adding repos to arcyd from pushing reviews so that they may be
separately measured.

Test Plan:
$ ./precommit.sh
arcyd-tester: accept reviews, complete happy path

Add the ability to _Workers to accept reviews, which means that we can
exercise the whole happy path.

Test Plan:
$ ./precommit.sh
TEMP: 5 workers