Make StatsD tests less flaky.

There have been a bunch of Jenkins failures lately where the StatsD
tests fail because they can't bind to their desired port. There's
nothing special about the particular port they're using, so now we let
the kernel pick an available one for us.

This also lets us get rid of a sleep() in the test that looked like an
attempt to alleviate EADDRINUSE errors, so now in the happy case, the
tests are a few fractions of a second faster.

Change-Id: Idee11349254107a59643539b1566f3588eee7ef4

test/unit/common/test_utils.py

@@ -984,9 +984,9 @@ class TestStatsdLogging(unittest.TestCase):
 
 class TestStatsdLoggingDelegation(unittest.TestCase):
     def setUp(self):
-        self.port = 9177
         self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
-        self.sock.bind(('localhost', self.port))
+        self.sock.bind(('localhost', 0))
+        self.port = self.sock.getsockname()[1]
         self.queue = Queue()
         self.reader_thread = Thread(target=self.statsd_reader)
         self.reader_thread.setDaemon(1)
@@ -1004,7 +1004,6 @@ class TestStatsdLoggingDelegation(unittest.TestCase):
         self.reader_thread.join(timeout=4)
         self.sock.close()
         del self.logger
-        time.sleep(0.15)  # avoid occasional "Address already in use"?
 
     def statsd_reader(self):
         while True: