Remove complexity when coding test results, runners and jobs.

- Change TestResult constructor signature to accept two parameters:
stream and args, everything else is passed inside args.

- Method test_runner() is now calling start_tests() and end_tests(),
  so it is the owner of all methods for test results.

-  Remove complexity of Job class by creating TestRunner class. 

Signed-off-by: Ruda Moura <rmoura@redhat.com>