mtree: Add more runtime package tag

When using pkgbase those empty directories aren't packaged otherwise.

Reviewed by:	bapt
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D20056

etc/mtree/BSD.sendmail.dist

@@ -6,7 +6,7 @@
 /set type=dir uname=root gname=wheel mode=0755
 .               nochange
     var             nochange
-        spool           nochange
+        spool           nochange tags=package=runtime
             clientmqueue    uname=smmsp gname=smmsp mode=0770
             ..
         ..

etc/mtree/BSD.usr.dist

@@ -428,9 +428,9 @@
         ..
         keys
             pkg
-                revoked
+                revoked tags=package=runtime
                 ..
-                trusted
+                trusted tags=package=runtime
                 ..
             ..
         ..

etc/mtree/BSD.var.dist

@@ -32,7 +32,7 @@
     ..
     crash
     ..
-    cron
+    cron                tags=package=runtime
         tabs            mode=0700
         ..
     ..
@@ -59,21 +59,21 @@
             ..
         ..
     ..
-    empty           mode=0555 flags=schg
+    empty           mode=0555 flags=schg tags=package=runtime
     ..
     games           gname=games mode=0775
     ..
     heimdal         mode=0700
     ..
-    log
+    log             tags=package=runtime
     ..
-    mail            gname=mail mode=0775
+    mail            gname=mail mode=0775 tags=package=runtime
     ..
     msgs            uname=daemon
     ..
     preserve
     ..
-    run
+    run             tags=package=runtime
         dhclient
         ..
         ppp             gname=network mode=0770
@@ -101,7 +101,7 @@
         ..
 /set gname=wheel
     ..
-    tmp             mode=01777
+    tmp             mode=01777 tags=package=runtime
         vi.recover      mode=01777
         ..
     ..