add c20 to conn scan

experiments/memcached_conn_scan.sh

@@ -9,7 +9,7 @@ run_exp() {
     memcached_init
 
     QPS=0
-    for CONNS in 10 40 80 160 240 320; do
+    for CONNS in 10 20 40 80 160 240 320; do
         export CONNS
         run_mutilate c$CONNS
     done