@Override
    public synchronized void close() {
      release();
      tearDownIfUnused();
    }
Decrement the user count and piggyback this to set expiry flag as well, then  teardown(), if conditions are met.
This *MUST* be called by anyone who uses this client.
hcatalog/core/src/main/java/org/apache/hive/hcatalog/common/HiveClientCache.java