Fix apparent typos in disk names

[mhucka]

Proposed Commit Message

Fix typos in disk names

The name `ephmeral0` appears in two places in this file, but based 
on the fact that `ephemeral0` is used elsewhere in the file, it is 
very likely that `ephmeral0` is actually a typo.

Additional Context

First spotted while reading the formatted docs at https://cloudinit.readthedocs.io/en/latest/topics/examples.html

Test Steps

This is a file of examples and (I think) not something that can be tested directly.

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[TheRealFalcon]

Thanks!