Various cosmetic improvements to run_tests.py

  -) Adding a new command line flag to be able to see which tests are passing.
  -) Adding more status when the tool is idle in forever mode.
  -) Adding a last status when the tool is finished so to avoid leaving the console in a weird state.
  -) Adding a status message in the forever mode if the previous run failed.
  -) Swapped the message and its explanation, so you don't have to scroll up to see which test failed.
  -) Fixed a race condition in the watch_dir.py code if a file is deleted during the loop.