Categorize remote task errors

This includes http 500 from workers, which is frequently returned if
they're in the process of shutting down.
Suppress exceptions closing record reader when handling an exception
Add release notes for 0.67
[maven-release-plugin] prepare release 0.67
[maven-release-plugin] prepare for next development iteration
Don't double count bytes and rows in RecordProjectOperator
Fix release notes for 0.67
Fix warnings in HiveBucketing
Fix handling of Hive tables bucketed on string
Add 0.68 release notes
Fix Hive bucketing test
[maven-release-plugin] prepare release 0.68
[maven-release-plugin] prepare for next development iteration
Increase parallelism in unit tests to 4
Add timestamp with time zone minus interval year month operator
Support explaining sampled queries
Move drop table logic to NativeMetadata
Static import query execution factories
Used shared executor for query execution
Rename InMemoryMetadata to TestingMetadata