Don't chwon partitions by default

  It kills the partitions and backups nodes.

slapos/cli/format.py

@@ -62,6 +62,7 @@ class FormatCommand(ConfigCommand):
 
         ap.add_argument('--alter_user',
                         choices=['True', 'False'],
+                        default=False,
                         help='Shall slapformat alter user database'
                              ' (default: %(default)s)')