Metrics collection

This script will collect a DC's total desired and actual when run. 

**TODO**:
- [ ] Collect pending also
- [ ] Tests
- [ ] Dump the data to Cloud metrics
Update:  Changes since results can probably be mixed with those from `get_all_server_details` right?  We probably only care about the deleted servers from the `changes-since` query, since any other changes will be already represented by the results from `get_all_server_details`?