Add utils.putFile() helper function.

Hmm... How about making `log` optional... In `client.py` we have:
```py
import logging
log = logging.getLogger(__name__)
log.setLevel(logging.DEBUG)
if os.environ.get('DEBUG_TASKCLUSTER_CLIENT'):
  log.addHandler(logging.StreamHandler())
log.addHandler(logging.NullHandler())
```

Granted I don't really understand logging in python... But couldn't we default log to `log` as created globally above? That way you can specify your own logger or just use the default one.