enhancement: make output summary more clear using colors

[jhump]

When the output is a terminal, the test runner could use colors to make the output summary maximally clear. For example, it could render the summary in green when there are no failures or red when there are failures.

This could also be used to improve any debug output from the client or server process, to make it clear which process emitted a line of output. For this the test runner could add a colorful prefix to each line, indicating which process printed the line, and the label could be use different colors for the client and server processes.