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/process.py

@@ -128,10 +128,13 @@ def _logged_communicate(pipe, log, input, extrafiles):
         pipe.stderr.close()
     return ''.join(outdata), ''.join(errdata)
 
-def run(cmd, input=None, log=None, extrafiles=[], **options):
+def run(cmd, input=None, log=None, extrafiles=None, **options):
     """Convenience function to run a command and return its output, raising an
     exception when the command fails"""
 
+    if not extrafiles:
+        extrafiles = []
+
     if isinstance(cmd, basestring) and not "shell" in options:
         options["shell"] = True