Set permissions on sahara cache

Signing certificate directory should have 700 mode.
Before the change it was created with 755.

As a visual impact this CR removes warning from 
keystonemiddleware.

Change-Id: I8483e73447348b9a9e33dfd382543978a70a9d43
Closes-Bug: #1387416
diff --git a/lib/sahara b/lib/sahara
index 5c7c253..42e8e01 100644
--- a/lib/sahara
+++ b/lib/sahara
@@ -104,6 +104,7 @@
     # Create auth cache dir
     sudo mkdir -p $SAHARA_AUTH_CACHE_DIR
     sudo chown $STACK_USER $SAHARA_AUTH_CACHE_DIR
+    sudo chmod 700 $SAHARA_AUTH_CACHE_DIR
     rm -rf $SAHARA_AUTH_CACHE_DIR/*
 
     configure_auth_token_middleware $SAHARA_CONF_FILE sahara $SAHARA_AUTH_CACHE_DIR