configdrive: Remove broken support for ec2 metadata

As it turns out, certain metadata is only present in the ec2 flavor
of metadata (e.g. public_ipv4) and other data is only present in
the openstack flavor (e.g. network_config). For now, just read the
openstack metadata.
Merge pull request #204 from crawford/configdrive

configdrive: Remove broken support for ec2 metadata