Fixes error when idle_timeout not defined in elb config

I hit an error when idle_timeout is not defined in the elb config:
```
$ cloudcaster.py infr/us-east-1-ops-stage.yaml
Traceback (most recent call last):
 File "/Users/robin/bin/cloudcaster.py", line 952, in <module>
   print "WARNING: %s timeout set to %s, and config says %s!!!!!!!" % (elb.name, elb_attr.connecting_settings.idle_timeout, confelb['idle_timeout'])
KeyError: 'idle_timeout'
```

This PR fixes it.