Document CloudStack data-server well-known hostname

[onitake]

Since 19.4, cloud-init supports a more reliable approach to obtain the CloudStack user-data server address than DHCP: Via the well-known data-server. hostname.

I think this deserves to be documented.

Commit when the feature was added: 9662a87

I also submitted a documentation PR to the CloudStack project, so they are in line: apache/cloudstack-documentation#132

[onitake]

I'm sorry, I thought I had already signed the CLA previously, but that wasn't the case.
I signed it now, please verify again.

[OddBloke]

Thanks for the contribution, and apologies for the time it's taken to get to this review! This looks good, and brings our documentation in line with what our code does, which is great! I have one inline suggested addition, which rounds out the full algorithm described.

Other than that: I can see your CLA signature, so all you need to do is add your GH username to tools/.github-cla-signers (in its alphabetically appropriate location) and that check will start passing.

Thanks again!

[onitake]

I added myself to the CLA list on this branch here, hope that's ok. I can create a separate PR if you prefer.

[OddBloke]

Thanks!