cleanvar: Fix startup order

Instead of having FILESYSTEMS require cleanvar, which doesn't really
make semantic sense, say that cleanvar needs to run before FILESYSTEMS.

MFC after:	3 days
Reviewed by:	imp
Differential Revision:	https://reviews.freebsd.org/D54118

libexec/rc/rc.d/FILESYSTEMS

@@ -3,7 +3,7 @@
 #
 
 # PROVIDE: FILESYSTEMS
-# REQUIRE: root mountcritlocal cleanvar tmp
+# REQUIRE: root mountcritlocal tmp var
 
 #	This is a dummy dependency, for services which require filesystems
 #	to be mounted before starting.  It also serves as the default early /

libexec/rc/rc.d/cleanvar

@@ -4,6 +4,7 @@
 
 # PROVIDE: cleanvar
 # REQUIRE: var
+# BEFORE:  FILESYSTEMS
 
 . /etc/rc.subr