#754 Clean up older power flow models

[Jason Fuller]

The older power flow models in the test folder need some clean up.

All of them are using the ID number for connections, some use numbers for names, and most are using voltage_A (even if there is not a phase A) rather than nominal_voltage.

These all need to be cleaned up to match our current power flow standard syntax to avoid confusion.

[Jason Fuller]

This should be done in all models using powerflow (whether in the powerflow folder or not) in branches 3.0 and newer, and trunk.