Add closed-loop conn vs throughput experiment

experiments/memcached_conn_scan.sh

+source "$EXP_ROOT/experiments/memcached.shared.sh"
+
+pre_start() {
+    memcached_pre_start
+    EXPERIMENT_NAME_EXT="t$THREADS"
+}
+
+run_exp() {
+    memcached_init
+
+    QPS=0
+    for CONNS in 10 40 80 160 240; do
+        export CONNS
+        run_mutilate c$CONNS
+    done    
+
+    memcached_deinit
+}
+
+post_start() {
+    memcached_deinit
+}