GH-17: Check if already registered a bit smarter.

TODO: Parse the UUID from config.pvs (prlctl doesn't seem to have a way to read
from it without the VM being registered) and use that instead of the file path.

But as a first iteration, the file path is guaranteed only to point to one VM.
Use UUIDs, not names.

Now it's working!
Universal 'read-*' functions. Refactoring
'read_all_names' fixed
Merge branch 'current'