SnapshotFileCache logs too many times if snapshot dir doesn't exists

On a cluster with "hbase.snapshot.enabled" true, the /hbase/.hbase-snapshot directory will not exists until a first snapshot will get created.

meanwhile the SnapshotFileCache (snapshot cleaner) will keep print out as error that the snapshot dir doesn't exists every N seconds ("hbase.master.hfilecleaner.plugins.snapshot.period")

LOG.error("Snapshot directory: " + snapshotDir + " doesn't exist");