"invalidate metadata" should only clear metadata for those tables the current user has access to

In impala, users often execute invalidate metadata (without any table) to clear the metadata cache. Since by default this affects all the databases/tables on the cluster, Sentry asks users to have privileges on the whole cluster (or "server" in Sentry's terminology) to execute this. However, this brings a huge inconvenience to customers, especially when they have multiple tables to refresh. They must do this one table by one.
From my point of view, when sentry is enabled, we should allow users to clear the metadata cache for all the tables he/she has access to, instead of asking for superuser privilege and clear all the tables metadata.