Code review comment for ~dojordan/cloud-init:azure-preprovisioning

There are some comments in line.
I'm not sure I fully understand all of this.

I could be wrong here, but I think you're using
bounce_network_with_azure_hostname in order to interact with IMDS_URL.

We have 2 ways now of brining up ephemeral networking for this purpose:
 a.) Chad has recently added code in the EC2 metadata service using cloudinit/net/dhcp.py .
 b.) the digital ocean datasource has code to negotiate a ipv4 link local address.

If 'b' is sufficient, I'd prefer that, but either one I'd prefer to the bounce_network_ which i think may actually not work for you if you rebased to trunk.

As mentioned in IRC, I'm still concerned about systemd giving up and deciding that boot has failed after some amount of time polling on a metadata service. As Douglas pointed out, cloud-init has timeouts set to 0 and is a 'oneshot', so *its* timeout is not an issue, but I think that things that it runs 'Before' or (pre-networking or other) might end up timing out.