Fix some tests and flake issues.

src/allmydata/test/common_util.py

@@ -1,6 +1,6 @@
 from __future__ import print_function
 
-import os, signal
+import os
 from random import randrange
 from six.moves import StringIO
 

src/allmydata/util/iputil.py

@@ -370,7 +370,7 @@ def listenOnUnused(tub, portnum=None):
     """
     portnum, endpoint = _foolscapEndpointForPortNumber(portnum)
     tub.listenOn(endpoint)
-    tub.setLocation("localhost:%d" % (portnum,))
+    tub.setLocation(native_str("localhost:%d" % (portnum,)))
     return portnum