Code review comment for lp:~leonardr/lazr.restful/cache-service-root

Nice branch. Conversation from IRC:

<allenap> leonardr: Is there any way config.active_versions could be empty?
<leonardr> allenap: no, that would prevent lazr.restful from starting up
<allenap> leonardr: Instead of having [604800, 3600], could you have a module-level constant like `HOUR = 3600 # seconds`, then the default can be specified as [7 * 24 * HOUR, 1 * HOUR]?
<leonardr> sure