MINOR: cache: Replace the "process-vary" option's expected values

Replace the <0/1> expected values of the process-vary option by a more
usual <on/off> pair.
diff --git a/reg-tests/cache/vary.vtc b/reg-tests/cache/vary.vtc
index 4e1958f..a840799 100644
--- a/reg-tests/cache/vary.vtc
+++ b/reg-tests/cache/vary.vtc
@@ -145,13 +145,13 @@
                total-max-size 3
                max-age 20
                max-object-size 3072
-               process-vary 1
+               process-vary on
 
        cache no_vary_cache
                total-max-size 3
                max-age 20
                max-object-size 3072
-               process-vary 0
+               process-vary off
 } -start