umqtt.simple: Add optional socket timeout to connect method.

If there are any network issues, mqtt will block on the socket
non-deterministically.  This commit introduces a `timeout` option which
can be used to set a finite timeout on the socket.  Upon any issue, mqtth
lib will throw exception.

Author: prabhu-yu

micropython/umqtt.simple/umqtt/simple.py

@@ -60,8 +60,9 @@ def set_last_will(self, topic, msg, retain=False, qos=0):
         self.lw_qos = qos
         self.lw_retain = retain
 
-    def connect(self, clean_session=True):
+    def connect(self, clean_session=True, timeout=None):
         self.sock = socket.socket()
+        self.sock.settimeout(timeout)
         addr = socket.getaddrinfo(self.server, self.port)[0][-1]
         self.sock.connect(addr)
         if self.ssl: