rocksock: skip shutdown on never-connected sockets

Track connection state with _connected flag. Only call
socket.shutdown() on successfully connected sockets.
Saves ~39s/session on workers (974k disconnect calls).

rocksock.py

@@ -242,6 +242,7 @@ class Rocksock():
 		target = RocksockProxy(host, port, RS_PT_NONE)
 		self.proxychain.append(target)
 		self.sock = None
+		self._connected = False
 		self.timeout = timeout
 
 	def _translate_socket_error(self, e, pnum):
@@ -302,15 +303,18 @@ class Rocksock():
 					select.select([], [self.sock], [])
 			"""
 
+		self._connected = True
 
 	def disconnect(self):
 		if self.sock is None: return
-		try:
-			self.sock.shutdown(socket.SHUT_RDWR)
-		except socket.error:
-			pass
+		if self._connected:
+			try:
+				self.sock.shutdown(socket.SHUT_RDWR)
+			except socket.error:
+				pass
 		self.sock.close()
 		self.sock = None
+		self._connected = False
 
 	def canread(self):
 		return select.select([self.sock], [], [], 0)[0]