Add pexp match otherwise rcctl stop vmd doesn't work. OK deraadt@

src/etc/rc.d/vmd

@@ -1,9 +1,11 @@
 #!/bin/sh
 #
-# $OpenBSD: vmd,v 1.1 2015/12/05 09:55:18 jasper Exp $
+# $OpenBSD: vmd,v 1.2 2015/12/16 14:21:28 jturner Exp $
 
 daemon="/usr/sbin/vmd"
 
 . /etc/rc.d/rc.subr
 
+pexp="vmd: parent.*"
+
 rc_cmd $1