HOTFIX: Ignore python metastore files in RAT checks.

This was causing some errors with pull request tests.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #393 from pwendell/hotfix and squashes the following commits:

6201dd3 [Patrick Wendell] HOTFIX: Ignore python metastore files in RAT checks.

.rat-excludes

@@ -39,4 +39,6 @@ work
 .*\.q
 golden
 test.out/*
-.*iml
\ No newline at end of file
+.*iml
+python/metastore/service.properties
+python/metastore/db.lck