Change the output of arc unit

  arc unit will now show the number of consecutive tests with the same
  result instead of printing a "." for each one. Due to the number of
  tests the "dots" didn't fit in one line any more. Furthermore the
  result list is shortened, only non passing tests or tests taking
  longer than a time threshold (50ms) will be reported (both to the user
  and to phabricator).

llvm-svn: 218826