Fix cli registration of expired machines

[Aluxima]

Fixes the CLI registration of machines already present in DB:

• Machines that logged out were not added to registration cache when joining again
• If the machine was still in cache (<15min after the first registration), expiry was not updated
• Registration cache was not cleaned up after successful machine registration

Checks that the machine is registered with the right namespace

• read the CONTRIBUTING guidelines
• raised a GitHub issue or discussed it on the projects chat beforehand
• added unit tests
• added integration tests
• updated documentation if needed
• updated CHANGELOG.md

Fixes #522

[Aluxima]

Fixes #749 as well

[juanfont]

This is an excellent catch! Thank you very much :)