adjust no_thread.vtc to pesi.set(thread, false) and make it tighter

src/tests/no_thread.vtc

@@ -131,7 +131,8 @@ server s21 {
 	txresp -body { <pre>Included file 19</pre> }
 } -start
 
-varnish v1 -arg "-p vcc_err_unref=off" -vcl+backend {
+# XXX why is max=3 not enough?
+varnish v1 -arg "-p thread_pools=1 -p thread_pool_min=3 -p thread_pool_max=4 -p vcc_err_unref=off" -vcl+backend {
 	import ${vmod_pesi};
 
 	sub vcl_backend_response {
@@ -206,6 +207,7 @@ varnish v1 -arg "-p vcc_err_unref=off" -vcl+backend {
 
 	sub vcl_deliver {
 		pesi.activate();
+		pesi.set(thread, false);
 	}
 } -start
 
@@ -378,6 +380,7 @@ varnish v1 -vcl+backend {
 
 	sub vcl_deliver {
 		pesi.activate();
+		pesi.set(thread, false);
 	}
 }