test.py: make test output brief&tabular
test.py: make test output brief&tabular

New format:

% ./test.py --verbose --mode=release
================================================================================
[N/TOTAL] TEST                                                 MODE   RESULT
------------------------------------------------------------------------------
[1/111]   boost/UUID_test                                    release  [ PASS ]
[2/111]   boost/enum_set_test                                release  [ PASS ]
[3/111]   boost/like_matcher_test                            release  [ PASS ]
[4/111]   boost/observable_test                              release  [ PASS ]
[5/111]   boost/allocation_strategy_test                     release  [ PASS ]
^C
% ./test.py foo
================================================================================
[N/TOTAL] TEST                                                 MODE   RESULT
------------------------------------------------------------------------------
[3/3]     unit/memory_footprint_test                          debug   [ PASS ]
------------------------------------------------------------------------------

scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla