Fix missing space in parameter description

... so that the words are properly rendered.

Trivial-Fix

Change-Id: Ib1db5e972765d4a01e59fde9dcad62d95d9c6f26
diff --git a/tempest/config.py b/tempest/config.py
index 0a084ea..8a532e9 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -647,7 +647,7 @@
     cfg.BoolOpt('image_caching_enabled',
                 default=False,
                 help=("Flag to enable if caching is enabled by image "
-                      "service, operator should set this parameter to True"
+                      "service, operator should set this parameter to True "
                       "if 'image_cache_dir' is set in glance-api.conf")),
     cfg.StrOpt('http_image',
                default='http://download.cirros-cloud.net/0.3.1/'