Don't rely blindly on the keys 'alt_device' and 'device_uuid'.

This will cause failures on systems not providing these keys such as
FreeBSD.
Merge pull request #12843 from eliasp/mount-keyerror

Don't rely blindly on the keys 'alt_device' and 'device_uuid'.
Arg definitions added to states.file.append
Pylint fix
Merge pull request #12852 from rallytime/pylint_fix

Pylint fix
Change lines to strings
Merge pull request #12851 from rallytime/file_append_docs

Arg definitions added to states.file.append