Get subprocess error output from shell command

[Gnarlodious]

I get it, you instantiate an object, call a method and get a tuple in
response. However, here is what I see:

>>> process.communicate()
(b'~/Library/Preferences/iCab/iCab 4 Bookmarks: Permission denied\n',
b'')

So all I get is the string and no error message, which is the same
thing I get with the simpler subprocess.call(). I can parse out the
error out and handle it if I need to. Is this a failing in the OSX
plutil tool?

-- Gnarlie