Migrate to localectl (if possible)

localectl is a tool which allows to configure the locale.
This patch migrates away from sysconfig towards localectl.

Legacy scripts (like the old UI) are not migrated.

rhbz#882206

Change-Id: Ieffc7915da82da7b5558d96e9c70e83d50108985
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>