pw_unit_test: Add logs to indicate test start/end
pw_unit_test: Add logs to indicate test start/end

Adds logs to test_runner.py that indicate the start/end of tests and
whether the test passed or failed.

The format is:
Test   8/365: [RUN] my_test
Test   8/365: [FAIL] my_test
...
Test 212/365: [RUN] my_other_test
Test 212/365: [PASS] my_other_test

Example:
20191126 11:44:41 AM INF Scanning for tests...
20191126 11:44:41 AM INF Found 4 test groups (10 tests).
20191126 11:44:41 AM INF Running test groups //pw_status:tests, //pw_preprocessor:tests, //pw_string:tests, //pw_span:tests
20191126 11:44:41 AM INF Test  1/10: [RUN] to_string_test
TEST - 2019-11-26 11:44:41 - INFO - Launching test binary out/stm32f429i-disc1/obj/pw_string/to_string_test.elf
TEST - 2019-11-26 11:44:41 - INFO - Flashing firmware to device...
TEST - 2019-11-26 11:44:43 - INFO - Successfully flashed firmware to device!
TEST - 2019-11-26 11:44:43 - INFO - Resetting device...
TEST - 2019-11-26 11:44:43 - INFO - Successfully reset device!
TEST - 2019-11-26 11:44:43 - INFO - Test passed!
20191126 11:44:43 AM INF Test  1/10: [PASS] to_string_test
20191126 11:44:43 AM INF Test  2/10: [RUN] status_test
TEST - 2019-11-26 11:44:43 - INFO - Launching test binary out/stm32f429i-disc1/obj/pw_status/status_test.elf
TEST - 2019-11-26 11:44:43 - INFO - Flashing firmware to device...
TEST - 2019-11-26 11:44:44 - INFO - Successfully flashed firmware to device!
TEST - 2019-11-26 11:44:44 - INFO - Resetting device...
TEST - 2019-11-26 11:44:44 - INFO - Successfully reset device!
TEST - 2019-11-26 11:44:44 - INFO - Test passed!
20191126 11:44:44 AM INF Test  2/10: [PASS] status_test

Change-Id: I916b3ea06a5a785a5d7f0f3653e96f8950037559

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed