Enhancement ModbusTcpClient Timeout (#140)

* Enhancement ModbusTcpClient Timeout

Today Scenario: when creating a TCP Client the Defaults timeout is Always used 
Enhancement Scenario: pool of clients with different timeouts (more like a UDP client that accepts different timeout on context)

* python 3 support

Author: semyont

pymodbus/client/sync.py

@@ -121,6 +121,7 @@ def __init__(self, host='127.0.0.1', port=Defaults.Port,
         :param host: The host to connect to (default 127.0.0.1)
         :param port: The modbus port to connect to (default 502)
         :param source_address: The source address tuple to bind to (default ('', 0))
+        :param timeout: The timeout to use for this socket (default Defaults.Timeout)
         :param framer: The modbus framer to use (default ModbusSocketFramer)
 
         .. note:: The host argument will accept ipv4 and ipv6 hosts
@@ -129,6 +130,7 @@ def __init__(self, host='127.0.0.1', port=Defaults.Port,
         self.port = port
         self.source_address = kwargs.get('source_address', ('', 0))
         self.socket = None
+        self.timeout  = kwargs.get('timeout',  Defaults.Timeout)
         BaseModbusClient.__init__(self, framer(ClientDecoder()), **kwargs)
 
     def connect(self):
@@ -140,7 +142,7 @@ def connect(self):
         try:
             address = (self.host, self.port)
             self.socket = socket.create_connection((self.host, self.port),
-                timeout=Defaults.Timeout, source_address=self.source_address)
+                timeout=self.timeout, source_address=self.source_address)
         except socket.error as msg:
             _logger.error('Connection to (%s, %s) failed: %s' % \
                 (self.host, self.port, msg))