Adding in cancel for a build that is building.

buildman/manager/noop_canceller.py

@@ -0,0 +1,8 @@
+class NoopCanceller(object):
+  """ A class that can not cancel a build """
+  def __init__(self, config=None):
+    pass
+
+  def try_cancel_build(self, uuid):
+    """ Does nothing and fails to cancel build. """
+    return False