tests/bench: run roundtrip.py a ton more to reduce variance

tests/bench/roundtrip.py

@@ -5,13 +5,22 @@ Measure latency of local RPC.
 import mitogen
 import time
 
+import ansible_mitogen.process
+ansible_mitogen.process.setup_gil()
+
+try:
+    xrange
+except NameError:
+    xrange = range
+
 def do_nothing():
     pass
 
 @mitogen.main()
 def main(router):
     f = router.fork()
+    f.call(do_nothing)
     t0 = time.time()
-    for x in range(1000):
+    for x in xrange(20000):
         f.call(do_nothing)
-    print '++', int(1e6 * ((time.time() - t0) / (1.0+x))), 'usec'
+    print('++', int(1e6 * ((time.time() - t0) / (1.0+x))), 'usec')