Use lstat() in do_copy_path and check for char and block devices

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
[libvirt] add missing os import

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
[plugin] handle lstat exceptions in do_copy_path()

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>