Avoid ResourceWarnings in ccbench

Tools/ccbench/ccbench.py

@@ -276,7 +276,7 @@ def _recv(sock, n):
     return sock.recv(n).decode('ascii')
 
 def latency_client(addr, nb_pings, interval):
-    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock:
         _time = time.time
         _sleep = time.sleep
         def _ping():
@@ -363,6 +363,7 @@ def run_latency_test(func, args, nthreads):
     for t in threads:
         t.join()
     process.wait()
+    sock.close()
 
     for recv_time, chunk in chunks:
         # NOTE: it is assumed that a line sent by a client wasn't received