Update base_scenario.py to handle race condition (#89)

* Update base_scenario.py

self.name for base_scenario leads to race conditions by only using seconds in the naming scheme

* ensured travis runs with python 3.6

* syntax fix

flow/scenarios/base_scenario.py

@@ -64,7 +64,7 @@ def __init__(self,
             Serializable.quick_init(self, locals())
 
         self.orig_name = name  # To avoid repeated concatenation upon reset
-        self.name = name + time.strftime("_%Y%m%d-%H%M%S")
+        self.name = name + time.strftime("_%Y%m%d-%H%M%S") + str(time.time())
 
         self.generator_class = generator_class
         self.vehicles = vehicles