Arcyd: don't clear bad_pre_review when retrying

To avoid thrashing the remote, don't clear the state of 'bad_pre_review'
branches before retrying them.  abdt_branch now supports moving directly
from bad_pre_review to one of the 'new review' states.

Test Plan:
Add extra run of arcyd to acceptance test
$ ./testbed/arcyd/acceptance_tests.sh
$ ./precommit.sh
Manually create and resolve an 'unknown user' review in
$ ./testbed/arcyd/test_shell.sh
paying attention to the tracking branches