Fix hypervisor command 'vm rename' not renaming it's files.

The vm name is used in the file names by default in hypervisor mode.
They we left alone and, with the vm stopped, the log file and the
lock file remain open.
This means that the vm would keep using 2 files with the old name.

Now it renames all related files. (best effort)
NOTE - will also rename unrelated files that have the old prefix.

Re-closes issue #21 - Renaming devices