[modules/cpu] Add initial version of CPU utilization module

Re-enable the CPU utilization module as proof-of-concept for the new
core engine.

see #23

tests/util.py

@@ -1,10 +1,29 @@
 # pylint: disable=C0103,C0111
 
+from bumblebee.output import Widget
+
+def assertWidgetAttributes(test, widget):
+    test.assertTrue(isinstance(widget, Widget))
+    test.assertTrue(hasattr(widget, "full_text"))
+
+class MockOutput(object):
+    def start(self):
+        pass
+
+    def stop(self):
+        pass
+
+    def draw(self, widgets, engine):
+        engine.stop()
+
+    def flush(self):
+        pass
+
 class MockWidget(object):
     def __init__(self, text):
         self._text = text
 
-    def text(self):
+    def full_text(self):
         return self._text
 
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