python 2.6 support

[eredding-rmn]

The .format() placeholders used throughout are not numerated, breaking compatibility with python 2.6.

relevant grep:
acky/api.py:61: return "{}: {}: {}".format(self.operation,
acky/api.py:77: log.debug("Calling {} action '{}'".format(self._service, operation))
acky/api.py:91: if r.startswith("{}-".format(continent))]
acky/ec2.py:21: if r['RegionName'].startswith("{}-".format(continent))]