Test driver: Implement different verbosities

Select verbosity with "make VERBOSE=n". Options so far:
 n=0: No per-test output
 n=1: Only failing test results
 n=2: As above, plus progress information (names of all tests)
 n=3: As aobve, plus commands called.
Default currently is n=3, although n=2 might be a nicer default.