hobo: handle new required --exists parameter (#7550)

wcs/ctl/check_hobos.py

@@ -42,6 +42,8 @@ class CmdCheckHobos(Command):
         Command.__init__(self, [
                 make_option('--ignore-timestamp', action='store_true',
                             dest='ignore_timestamp', default=False),
+                make_option('--exists', action='store_true',
+                            dest='exists', default=False),
                 ])
 
     def execute(self, base_options, sub_options, args):
@@ -72,6 +74,12 @@ class CmdCheckHobos(Command):
 
         pub.app_dir = os.path.join(global_app_dir,
                 self.get_instance_path(service))
+        if sub_options.exists:
+            if os.path.exists(pub.app_dir):
+                sys.exit(0)
+            else:
+                sys.exit(1)
+
         if not os.path.exists(pub.app_dir):
             print 'initializing instance in', pub.app_dir
             os.mkdir(pub.app_dir)