abdi_processrepoarglist: log cycle stats to debug
abdi_processrepoarglist: log cycle stats to debug

In addition to reporting cycle stats via the external reporter, also log
cycle stats to the debug log. Use the prefix 'cycle-stats:' so they're
easily grep-able.

This addition will make it easy to extract an impression of recent
performance over time, alongside the significant other events of the
time.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/test_shell.sh
    $ tail -f ../arcyd/var/log/debug
    .. observe cycle stats ..

aevri/phabricator-tools,bloomberg/phabricator-tools,aevri/phabricator-tools,bloomberg/phabricator-tools,aevri/phabricator-tools,kjedruczyk/phabricator-tools,cs-shadow/phabricator-tools,kjedruczyk/phabricator-tools,cs-shadow/phabricator-tools,cs-shadow/phabricator-tools,cs-shadow/phabricator-tools,aevri/phabricator-tools,kjedruczyk/phabricator-tools,cs-shadow/phabricator-tools,kjedruczyk/phabricator-tools,kjedruczyk/phabricator-tools,bloomberg/phabricator-tools,bloomberg/phabricator-tools,bloomberg/phabricator-tools,aevri/phabricator-tools