Measure static guard nodes with OnionPerf
The specifications for measuring this are as follows:
- OP should measure one guard or set of guards at a time. It could use NumEntryGuards in the torrc file to support more than 1 guard
- A new guard/set of guards must be chosen after a day of measurement
- All CBT data must be erased when choosing a new set of guards, after day of measurements (at UTC midnight). This could mean erasing or replacing the state file for CBT.