Fix for issue 1441

[pbaughman]

Suggested fix for #1441

Use the logger.Handler's format method so that by default stack traces
are included in the log message if exc_info is set on the LogRecord

[tfoote]

Hmm there was a rosbag error off by one on stretch only that seems like it should be unreleated.

1967 != 1968
  File "/usr/lib/python2.7/unittest/case.py", line 329, in run
    testMethod()
  File "/tmp/catkin_workspace/src/ros_comm/test/test_rosbag/bag_migration_tests/test/random_play.py", line 113, in test_random_play
    self.assertEqual(len(self.input), rmg.message_count())
  File "/usr/lib/python2.7/unittest/case.py", line 513, in assertEqual
    assertion_func(first, second, msg=msg)
  File "/usr/lib/python2.7/unittest/case.py", line 506, in _baseAssertEqual
    raise self.failureException(msg)

@ros-pull-request-builder retest this please.

[tfoote]

The CI passed on a retest.

[dirk-thomas]

Thank you for the improvement.