Metrics collection

This script will collect a DC's total desired and actual when run. 

**TODO**:
- [x] Collect pending also
- [ ] Tests
- [ ] Dump the data to Cloud metrics
I have no idea how to name this in both a clear and succinct manner.  :(  The docstring maybe could state that this returns all the groups for all the tenants, even if each tenant has more groups than the batch size?