Invert the --skip-scrub test.

The $opt_skip_scrub option was tested incorrectly, which caused
the --skip-scrub option to operate opposite intent.

Author: dajhorn

src/zfs-auto-snapshot.sh

@@ -346,7 +346,7 @@ do
 	done
 
 	# Exclude objects in scrubbing pools if the --skip-scrub flag is set.
-	test -z "$opt_skip_scrub" && for jj in $ZPOOLS_SCRUBBING
+	test -n "$opt_skip_scrub" && for jj in $ZPOOLS_SCRUBBING
 	do
 		# Ibid regarding iii.
 		jjj="$jj/"