Python 3 Fix: use bytesIO instead of cStringIO

With the move from cStringIO to the io module, use six..BytesIO as
a python 3 compatible version of cStringIO module.

Change-Id: Idc62004b28f79c5ef2e3aa0250fce30882f4be65

zuul/cmd/__init__.py

@@ -14,8 +14,8 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import six
 from six.moves import configparser as ConfigParser
-import cStringIO
 import extras
 import logging
 import logging.config
@@ -47,7 +47,7 @@ def stack_dump_handler(signum, frame):
             yappi.start()
         else:
             yappi.stop()
-            yappi_out = cStringIO.StringIO()
+            yappi_out = six.BytesIO()
             yappi.get_func_stats().print_all(out=yappi_out)
             yappi.get_thread_stats().print_all(out=yappi_out)
             log.debug(yappi_out.getvalue())