adding the exception RecordNotFound to UUID find #11957

Basic change to handle UUIDS exception to fix https://github.com/rails/rails/issues/11957 and those related.
Ex. 
User.find(some-non-uuid)
will trigger a RecordNotFound instead of PG::InvalidTextRepresentation
I created an app to test this as well:
https://github.com/joseluistorres/my-test-app

Please provide feedback, thanks!

We could @rafaelfranca , if we know that the query to be done was originated from an AR::core.find otherwise if I left pgerror validation this will trigger the RecordNotFound in an UPDATE or other DB operations. I've been trying to dig in the PostgresAdapter to see if I can know that data, or something else? you have any suggestion to where I can read? Thanks!