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.

micropython/umqtt.simple/manifest.py

@@ -1,4 +1,4 @@
-metadata(description="Lightweight MQTT client for MicroPython.", version="1.4.0")
+metadata(description="Lightweight MQTT client for MicroPython.", version="1.5.0")
 
 # Originally written by Paul Sokolovsky.
 

micropython/umqtt.simple/umqtt/simple.py

@@ -60,8 +60,9 @@ class MQTTClient:
         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: