Have a consistent way of recording exception and status of span

[lzchen]

Following #1282,

Find a consistent way of recording exceptions from spans and instrumentations.

Currently, we have this and this both of which are needed depending on how the user creates the span. We should find a consistent way for all instrumentations to a) set error status and description on an error if caught and b) call record_exception when any of these happen.

[Oberon00]

When cleaning this up, also consider setting exception.escaped to True for record_exception, since in __exit__ we know that the exception escapes the span. See https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/semantic_conventions/exceptions.md#attributes