Flush the auth token table on resetUid

This prevents old stale auth tokens from sticking around after clearing.

Change-Id: I92e48b6d8cdba92cbc70f718cb45a4d96bd12900
diff --git a/keystore/auth_token_table.h b/keystore/auth_token_table.h
index 102e6e4..7a9cc34 100644
--- a/keystore/auth_token_table.h
+++ b/keystore/auth_token_table.h
@@ -95,6 +95,8 @@
      */
     void MarkCompleted(const keymaster_operation_handle_t op_handle);
 
+    void Clear();
+
     size_t size() { return entries_.size(); }
 
   private: