Support "nocloud"

https://cloudinit.readthedocs.io/en/latest/topics/datasources/nocloud.html

• tiny-cloud-early would mount a metadata volume
• /lib/tinycloud/nocloud/imds would reference information from metadata YAML files instead of attempting to contact an IMDS service which doesn't exist

The challenge will be to implement a tiny YAML parser. We may be able to get by with something "good enough" to get just the metadata we're interested in, in order to get the information we need.

@ncopa