The '-realtime mlock' cmd line argument was introduced in QEMU
commit v1.5.0-rc0~190 which matches minimal QEMU version we
require. Therefore, the capability will always be present.

Apparently, nearly none of our xml2argv test cases had the
capability hence slightly bigger change under qemuxml2argvdata/.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>