Make pylint aware of "stateless_property" decorator

Mark it as defining property, so pylint knows accessing those properties
is about the value, not the function.

(cherry picked from commit 3362ffc)

.pylintrc

@@ -1,6 +1,7 @@
 [MASTER]
 persistent=no
 ignore=tests
+init-hook="import astroid.bases; astroid.bases.POSSIBLE_PROPERTIES.add('stateless_property')"
 
 [MESSAGES CONTROL]
 # abstract-class-little-used: see http://www.logilab.org/ticket/111138

qubes/vm/qubesvm.py

@@ -2137,7 +2137,7 @@ def is_qrexec_running(self, stubdom=False):
             :py:obj:`False` otherwise.
         :rtype: bool
         """
-        if self.xid < 0:  # pylint: disable=comparison-with-callable
+        if self.xid < 0:
             return False
         name = self.name + '-dm' if stubdom else self.name
         return os.path.exists('/var/run/qubes/qrexec.%s' % name)
@@ -2275,7 +2275,6 @@ def start_time(self):
     def icon(self):
         """freedesktop icon name, suitable for use in
         :py:meth:`PyQt4.QtGui.QIcon.fromTheme`"""
-        #  pylint: disable=comparison-with-callable
         raw_icon_name = self.label.name
         if self.klass == 'TemplateVM':
             return 'templatevm-' + raw_icon_name