more polishing of the real world vcl code

- minimum ttl of 10s for HFM objects
- simplify the X-TTL code
- show is_esi() example

src/tests/realworld.vtc

@@ -124,6 +124,9 @@ varnish v1 \
 				unset beresp.http.X-TTL;
 			} else {
 				set beresp.uncacheable = true;
+				if (beresp.ttl < 10s) {
+				    set beresp.ttl = 10s;
+				}
 			}
 			return (deliver);
 		}
@@ -143,16 +146,14 @@ varnish v1 \
 	}
 
 	sub br_deliver {
+		unset resp.http.X-TTL;
+		# for ESI:
+		# if (objesi.is_esi() || obj.uncacheable)
 		if (obj.uncacheable) {
 			# NOP
 		} else if (local.socket == "self_plain") {
-			if (obj.uncacheable) {
-				unset resp.http.X-TTL;
-			} else {
-				set resp.http.X-TTL = obj.ttl;
-			}
+			set resp.http.X-TTL = obj.ttl;
 		} else {
-			unset resp.http.X-TTL;
 			if (resp.http.Vary ~ "\bV-A-E\s*,") {
 				set resp.http.Vary = regsub(resp.http.Vary,
 				    "\bV-A-E\s*,\s*", "");