Added LED strand test to LED.py

Added a test routine to led.py to do a simple LED strand test. The
strand test scrolls a red, green, and blue pixel across the LED strip
forever.

python/led.py

@@ -27,6 +27,19 @@ def update():
     _sock.sendto(m.encode(), (config.UDP_IP, config.UDP_PORT))
 
 
+# Execute this file to run a LED strand test
+# If everything is working, you should see a red, green, and blue pixel scroll
+# across the LED strip continously
 if __name__ == '__main__':
+    import time
+    # Turn all pixels off
     pixels *= 0
-    update()
+    pixels[0, 0] = 255 # Set 1st pixel red
+    pixels[1, 1] = 255 # Set 2nd pixel green
+    pixels[2, 2] = 255 # Set 3rd pixel blue
+    print('Starting LED strand test')
+    while True:
+        pixels = np.roll(pixels, 1, axis=1)
+        update()
+        time.sleep(0.2)
+