Improve log errors

[Siecje]

With the current log error call log message sent to Sentry are being truncated.

https://github.com/graphql-python/graphql-core/blob/master/graphql/execution/utils.py#L155

https://forum.sentry.io/t/tracebacks-are-being-truncated/7304/2

One solution is to use log.error() with exc_info=True.

https://forum.sentry.io/t/some-stack-traces-are-truncated/7309