Fix corner case for cache-dir where the value isn't in the env.

W/out it in the env, this can lead to downstream getting annoyed.

BUG=chromium-os:34450
TEST=manual

Change-Id: I4cdf38dc88c77981616e3de8525f7558aa5cc552
Reviewed-on: https://gerrit.chromium.org/gerrit/34711
Tested-by: Brian Harring <ferringb@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Ready: Brian Harring <ferringb@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index cf79264..29c355e 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -1068,6 +1068,7 @@
     else:
       options.cache_dir = parser.FindCacheDir(parser, options)
     options.cache_dir = os.path.abspath(options.cache_dir)
+    parser.ConfigureCacheDir(options.cache_dir)
 
   osutils.SafeMakedirs(options.cache_dir)