Add Python 2.6 support for sim runner

Currently, the simulation runner does not work with Python 2.6. It would be fairly trivial to add support if we simply replace this:

```
if sys.version_info.major == 3:
```

with something like this:

```
if sys.version[0] == "3":
```

I don't believe there would be any serious downsides, and it should work with Python 2.6 and up (as of now, we support 2.7 and up).
