Keywords does not verify whether the `.img` file exists.

[Psotas]

@keyword("Mount Image PiKVM") and @keyword("Upload Image PiKVM") pass, even if they don't upload and mount the image.

I noticed this problem when, when testing on a branch, we used the old pikvm-rest-api repo and these keywords had a different number of arguments.

Solution(?):
Using the API, use Get MSD state to check if given steps the image file is deleted/added.