Yield the thread before returning from view loop

The inner loop trying to read the multi-stream-sink-view was hogging the
GIL. This resulted in the thread that was reading from the socket not
getting scheduled often enough, which lead to timeout errors on tests
that relied on data actually being read.

testing/tools/integration/control.py

@@ -143,20 +143,22 @@ def run(self):
         view = self.sink.view(blocking=False)
         msgs = 0
         while not self.stopped():
+            if not self.values:
+                self.stop()
+                logging.debug("SinkAwait complete with remaining values: {}"
+                        .format(self.values))
+                break
             msg = next(view)
-            processed = self.func(msg) if msg is not None else None
-            if processed:
+            if msg is not None:
                 msgs += 1
+                processed = self.func(msg)
                 if processed in self.values:
                     self.values.discard(processed)
                     logging.debug("{} matched on value {!r}."
                                    .format(self.name,
                                            processed))
-            if not self.values:
-                self.stop()
-                logging.debug("SinkAwait complete with remaining values: {}"
-                        .format(self.values))
-                break
+            else:
+                time.sleep(0.001)
             if time.time() - started > self.timeout:
                 self.error = TimeoutError('{}: has timed out after {} seconds'
                                           ', with {} messages. before '

testing/tools/integration/end_points.py

@@ -178,6 +178,7 @@ def __next__(self):
                     # sleep after a full round on all keys produces no value
                     time.sleep(0.001)
                 else:
+                    time.sleep(0.001)
                     return None
             # implicit:  continue