kvm tools: Add missing space after kernel params

kvm tools: Add missing space after kernel params

Add missing space so that user-provided kernel params
will be properly concatenated to default params.

Instead of just adding a space at the end, add it with
a separate strcat(), since it's not the first (and wouldn't
have been the last) time a space wasn't added.

Reported-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>