Add basic integration tests.

This attempts to get the first page of results from every collection
exposed through a service (e.g. S3 buckets, EC2 instances, etc).
SQS dead letter queues are skipped because they require a parameter,
and we skip an EC2 collection that takes ~30 seconds because it's
a huge response.
Merge pull request #25 from boto/integ

Add basic integration tests.