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!

I tried this yesterday:
```
def find(*ids)
....
begin
  record = s.execute([id], self, connection).first
rescue ActiveRecord::StatementInvalid => e
  raise ActiveRecord::RecordNotFound
end
...
```
I thought it will crash with others DBs no? Perhaps adding a second validation inside the rescue?