Custom KPI clutter in examples

[Jaap-Neven]

Problem description

When defining custom KPIs in one of the examples (using interface.py), it prints each custom KPI every step of the loop, which causes clutter such that important test case information is lost in the runtime environment. Example of only part of the print output:

Proposed fix

At the end of the code, print the custom KPIs as a pandas dataframe, as shown in the figure below:

Can implement together with #688

[dhblum]

Closed by #697.