bitbake: Fix default function parameter assignment to a list

With python you should not assign a list as the default value of a
function parameter - because a list is mutable, the result will be that
the first time a value is passed it will actually modify the default.
Reference:

http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments

(Bitbake rev: 7859f7388f2e3f675d0e1527cfde18625f36f637)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/process.py

@@ -124,8 +124,10 @@ class ProcessServer(Process, BaseImplServer):
         self.command_channel.close()
         self.cooker.shutdown(True)
 
-    def idle_commands(self, delay, fds = []):
+    def idle_commands(self, delay, fds=None):
         nextsleep = delay
+        if not fds:
+            fds = []
 
         for function, data in self._idlefuns.items():
             try: