avro

AVRO-3065: Introduce UUID logical type to Python implementation (#1148)

* AVRO-3065 Introduce UUID logical type to Python implementation

This PR introduces the UUID logical type implementation that was missing in the
primary python implementation. A new `UUIDSchema` has been introduced, and test
cases for schema and io have been updated.

Closes: https://issues.apache.org/jira/browse/AVRO-3065

* Fix lint issue in schema.py

* AVRO-3065 Accept UUID values of different versions

This commit changes UUID validation to accept UUID values of any
version, instead of being locked to version 4.

Also, return `None` on failed validation instead of `False`, for
consistency with others.