Change httpd Keystone log to keystone.log

The normal extension for log files is .log. Log rotation should
work because the extension is as expected.

Change-Id: Ia5e42ea9d953e8395b86ab58cdef6c2d852efc94
Related-Bug: #1359995
diff --git a/lib/keystone b/lib/keystone
index 547646a..07fee6e 100644
--- a/lib/keystone
+++ b/lib/keystone
@@ -467,7 +467,7 @@
 
     if [ "$KEYSTONE_USE_MOD_WSGI" == "True" ]; then
         restart_apache_server
-        screen_it key "cd $KEYSTONE_DIR && sudo tail -f /var/log/$APACHE_NAME/keystone"
+        screen_it key "cd $KEYSTONE_DIR && sudo tail -f /var/log/$APACHE_NAME/keystone.log"
     else
         # Start Keystone in a screen window
         screen_it key "cd $KEYSTONE_DIR && $KEYSTONE_DIR/bin/keystone-all --config-file $KEYSTONE_CONF --debug"