[rqd] Fix keys not iterable since it's a built-in function. (#1564)

**Link the Issue(s) this Pull Request is related to.**
This fixes an bug introduced with #1554 

**Summarize your change.**
It fixes a small bug that hinders `rqd` to actually run any jobs. It
probably didn't get chaught due to the unittests for rqd not working
properly.

rqd/rqd/rqcore.py

@@ -1091,7 +1091,7 @@ def sanitizeFrames(self):
         Iterate over the cache and update the status of frames that might have
         completed but never reported back to cuebot.
         """
-        for frameId in list(self.__cache.keys):
+        for frameId in list(self.__cache.keys()):
             runningFrame = self.__cache[frameId]
             # If the frame was marked as completed (exitStatus) and a report has not been sent
             # try to file the report again