wrap boto.utils.get_instance_metadata to ensure non-lazy loading
newer versions of boto lazily load the metadata from the ec2
metadata service. Here, we:
1. Add a ec2_utils module that checks which version of boto is being used and
under the right versions the metadata dictionary will be expanded.
2. Use this new ec2_utils module in the cloudstack and ec2
datasources as there entrypoints into boto.
3. Add a dependency on python-pkg-resources (from pkg_resources import
parse_version) to determine the boto version.