Do not run _rc_parse_conf of /var/run/rc.d/foobar on "start".

This is needed in case a foobar fails to start but still returns 0. Changing its
flags (in rc.conf.local) would then get ignored because of this cache (which is
around to handle stop/check/reload on flags changes).
claudio@ reported this issue when struggling with prometheus several weeks ago

src/etc/rc.d/rc.subr

@@ -1,4 +1,4 @@
-#	$OpenBSD: rc.subr,v 1.132 2019/09/07 10:02:19 ajacoutot Exp $
+#	$OpenBSD: rc.subr,v 1.133 2020/02/22 18:58:13 ajacoutot Exp $
 #
 # Copyright (c) 2010, 2011, 2014-2017 Antoine Jacoutot <ajacoutot@openbsd.org>
 # Copyright (c) 2010, 2011 Ingo Schwarze <schwarze@openbsd.org>
@@ -201,7 +201,7 @@ rc_cmd() {
 
 	[ -n "${_RC_DEBUG}" ] || _n="-n"
 
-	_rc_do _rc_parse_conf ${_RC_RUNFILE}
+	[[ ${1} == start ]] || _rc_do _rc_parse_conf ${_RC_RUNFILE}
 
 	case "$1" in
 	check)