Fix track_exception for non-str exception args

exc_value.args may contain members that aren't strings, which will cause ''.join() to raise an error. Calling str on the exception will produce the message as intended by the exception creator, which for most standard exceptions is the same as ''.join(args).

applicationinsights/TelemetryClient.py

@@ -98,7 +98,7 @@ class TelemetryClient(object):
         details.id = 1
         details.outer_id = 0
         details.type_name = type.__name__
-        details.message = ''.join(value.args)
+        details.message = str(value)
         details.has_full_stack = True
         counter = 0
         for tb_frame_file, tb_frame_line, tb_frame_function, tb_frame_text in traceback.extract_tb(tb):