Allow applications postfix to be configured

The postfix _hosts appended to applications to create host groups is now
configurable.

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/config.py b/config.py
index 58c29c5..1a3c603 100644
--- a/config.py
+++ b/config.py
@@ -33,6 +33,9 @@
                              default=defaults.get('pretty_print', False),
                              action="store_true",
                              help='try to make the output prettier [%default]')
+    options_group.add_option('--applications-postfix', dest='applications_postfix',
+                             default=defaults.get('applications_postfix', '_hosts'),
+                             help="the postfix to apply to groups made from applications ['%default']")
     parser.add_option_group(options_group)
 
     run_modes = optparse.OptionGroup(parser, 'Modes',