Print each test duration with results

[kuenishi]

For Riak CS, we had been running all integration test for each pull request. But recently the more tests we add the longer whole run takes. The purpose of this change is to have a rough view on which test takes long time without running each tests manually. Although there could be many other aspects to see what is slow, this is the most important aspect, I believe. The result will be like this:

Test Results:
user_test-cs_multi_backend                  : pass (  62.5 sec)
upgrade_downgrade_test-cs_multi_backend     : pass ( 409.6 sec)
too_large_entity_test-cs_multi_backend      : pass (  59.1 sec)
storage_stats_test_2-cs_multi_backend       : pass (  68.2 sec)
storage_stats_test-cs_multi_backend         : pass (  67.7 sec)
storage_stats_detailed_test-cs_multi_backend: pass (  83.1 sec)
stats_test-cs_multi_backend                 : pass (  59.8 sec)
stanchion_switch_test-cs_multi_backend      : pass (  67.1 sec)
sibling_benchmark-cs_multi_backend          : pass (  87.9 sec)
select_gc_bucket_test-cs_multi_backend      : pass (  10.4 sec)
repl_v3_test-cs_multi_backend               : pass ( 203.7 sec)
regression_tests_2-cs_multi_backend         : pass ( 126.8 sec)
regression_tests-cs_multi_backend           : pass (  59.0 sec)
put_copy_test-cs_multi_backend              : pass (  60.5 sec)
object_get_test-cs_multi_backend            : pass (  63.6 sec)
object_get_conditional_test-cs_multi_backend: pass (  59.7 sec)
mp_upload_test-cs_multi_backend             : pass (  70.9 sec)
migration_mixed_test-cs_multi_backend       : pass ( 385.3 sec)
migration_15_to_20_test-cs_multi_backend    : pass ( 352.4 sec)
mb_trans_test-cs_multi_backend              : pass ( 106.5 sec)
mb_trans2_test-cs_multi_backend             : pass ( 340.9 sec)
mb_pg_test-cs_multi_backend                 : pass ( 222.0 sec)
mb_disjoint_test-cs_multi_backend           : pass (  59.4 sec)
list_objects_v2_test-cs_multi_backend       : pass ( 395.0 sec)
list_objects_test-cs_multi_backend          : pass (  73.8 sec)
legacy_s3_rewrite_test-cs_multi_backend     : pass (  74.4 sec)
gc_tests-cs_multi_backend                   : pass ( 131.6 sec)
external_client_tests-cs_multi_backend      : fail (1077.4 sec)
cs743_regression_test-cs_multi_backend      : pass (  80.8 sec)
buckets_test-cs_multi_backend               : pass (  60.6 sec)
block_audit_test-cs_multi_backend           : pass (  10.4 sec)
auth_bypass_test-cs_multi_backend           : pass (  57.8 sec)
active_delete_test-cs_multi_backend         : pass (  92.3 sec)
access_stats_test-cs_multi_backend          : pass (  80.8 sec)
---------------------------------------------
1 Tests Failed
33 Tests Passed

Making all tests containerised and parallel run would be the right answer for that, but we'll need a big bunch of energy and hustle to realise it.