pc-testdev: use HTTPS git URL

When you clone the repository without previous commit history, 'git://'
doesn't protect from man-in-the-middle attacks.  HTTPS is more secure
since the client verifies the server certificate.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Suggested-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20181108111531.30671-7-stefanha@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/misc/pc-testdev.c

@@ -32,7 +32,7 @@
  * -kernel /home/lmr/Code/virt-test.git/kvm/unittests/msr.flat
  *
  * Where msr.flat is one of the KVM unittests, present on a separate repo,
- * git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git
+ * https://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git
 */
 
 #include "qemu/osdep.h"