SchemaValidationUtil#hasErrors recursion bug

The FS SchemaValidationUtil#hasErrors method may receive recursive structures, so we need to keep track of visited nodes and exit. This is currently preventing customers from evolving schemas. The work-around is to update the schema by hand by replacing schema.avsc in a dataset's .metadata folder or for Hive, running one of these commands depending on whether avro.schema.literal or avro.schema.url is used:

hive> alter table table_name set TBLPROPERTIES('avro.schema.literal'='<new schema literal>');
hive> alter table table_name set TBLPROPERTIES('avro.schema.url'='hdfs:/schemas/updated_schema.avsc');