Do not restore SELinux settings that were not backed up

https://fedorahosted.org/freeipa/ticket/4678

Reviewed-By: Petr Vobornik <pvoborni@redhat.com>

ipaplatform/base/tasks.py

@@ -152,7 +152,8 @@ class BaseTaskNamespace(object):
 
         :param required_settings: A dictionary mapping the boolean names
                                   to desired_values.
-                                  The desired value can be 'on' or 'off'.
+                                  The desired value can be 'on' or 'off',
+                                  or None to leave the setting unchanged.
 
         :param backup_func: A function called for each boolean with two
                             arguments: the name and the previous value

ipaplatform/redhat/tasks.py

@@ -363,6 +363,8 @@ class RedHatTaskNamespace(BaseTaskNamespace):
         updated_vars = {}
         failed_vars = {}
         for setting, state in required_settings.iteritems():
+            if state is None:
+                continue
             try:
                 (stdout, stderr, rc) = ipautil.run([paths.GETSEBOOL, setting])
                 original_state = stdout.split()[2]