scoutfs-tests: use fallocate to get large extent

The simple-release-extents test wanted to create a file with a single
large extent, but it did it with a streaming write.  While we'd like
our data allocator to create a large extent from initial writes, it
certainly doesn't guarantee it.  Fallocate is much more likely to
createa a large extent.

Signed-off-by: Zach Brown <zab@versity.com>

tests/tests/simple-release-extents.sh

@@ -13,7 +13,10 @@ create_file() {
 	local file="$1"
 	local size="$2"
 
-	t_quiet xfs_io -f -c "pwrite 0 $size" "$file"
+	t_quiet xfs_io -f \
+		-c "falloc 0 $size" \
+		-c "pwrite 0 $size" \
+		"$file"
 }
 
 # if vers is "stat" then we ask stat_more for the data_version