Fix regression by forcing no IMDS ssh keys

[trstringer]

Proposed Commit Message

Fix regression with handling of IMDS ssh keys.

With the changes for ssh public keys to be retrieved from IMDS as a first option, when a key is passed through not in the raw ssh public key format it causes an issue and the key is not added to the user's authorized_keys file.

This PR will temporarily disable this behavior until a permanent fix is put in place.

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

[OddBloke]

Thanks for this fix, Thomas! We'll need to discuss how to remediate this problem in a longer-term fashion, but this fix addresses our immediate need.

I have one important question inline: I want to make sure that the logging/diagnostics are aligned with your expectations. (I also have a side note, which doesn't really need addressing here.)

[OddBloke]

Thanks for the clarifications! I'm happy with this code. I'm now performing some testing locally, I will approve once I've confirmed this works.

[OddBloke]

I've confirmed that this fixes the issue using the test that I have just proposed for review in #761 (your review over there would be appreciated!). Thanks!

[trstringer]

Thanks, @OddBloke!