cf-renewer sends duplicate docs to collector

[hsiliev]

Now cf-renewer reads all started apps from the last month and tries to send the refreshed usage to the current month.

This loads Abacus unnecessarily. One solution would be to store a flag in the carry-over DB that shows if the usage is already processed or not.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/142941759

The labels on this github issue will be updated when the story is started.