run-tests: use items() instead of iteritems()

This fixes the python3.5 build. We'll presumably want to build our own
helper function or use 2to3 for this on the main source tree, but for
run-tests we want a single-source version that works in 2.6 and 3.5.

tests/run-tests.py

@@ -1711,7 +1711,7 b' class TestRunner(object):'
                     if e.errno != errno.ENOENT:
                         raise
                     return -1e9 # file does not exist, tell early
-                for kw, mul in slow.iteritems():
+                for kw, mul in slow.items():
                     if kw in f:
                         val *= mul
                 return val