oem-ec2-compat: Check for metadata service and config drive

Allow the existing media-configdrive.service unit to run cloudinit on
/media/configdrive. If there is no such mount, ec2-cloudinit-metadata.service
will run cloudinit on the metadata service instead. This will allow these
instances to work with both a configdrive or metadata service. Additionally,
get rid of the helper scripts since cloudinit can read from the metadata
service now.
Leave this name the same so we don't alter the hacky ordering behavior. That ordering hack helps avoid a race between checking /media/configdrive and the mask.