pulseaudio: hides some error messages

When we move the sink of an application, it can fail, then pacmd
print error message on stdout, breaking the i3pystatus json.

This changes hides these messages since their are not really usefull.

i3pystatus/pulseaudio/__init__.py

@@ -1,3 +1,4 @@
+import os
 import re
 import subprocess
 
@@ -211,7 +212,11 @@ class PulseAudio(Module, ColorRangeModule):
                                                   universal_newlines=True)
             for input_index in re.findall('index:\s+(\d+)', sink_inputs):
                 command = "pacmd move-sink-input {} {}".format(input_index, next_sink)
-                subprocess.call(command.split())
+
+                # Not all applications can be moved and pulseaudio, and when
+                # this fail pacmd print error messaging
+                with open(os.devnull, 'w') as devnull:
+                    subprocess.call(command.split(), stdout=devnull)
         subprocess.call("pacmd set-default-sink {}".format(next_sink).split())
 
     def switch_mute(self):