Change CommadFailedEvent.Failure type to error

[jtagcat]

+ gofmt

To get string, .Error() can be called on error.

ServerHeartbeatFailedEvent.Failure is already of type error.

Background & Motivation

I wanted to use error value. Couldn't. ServerHeartbeatFailedEvent.Failure already uses error.

[jtagcat]

OK make fmt
OK make lint
make test: go.mongodb.org/mongo-driver/mongo/integration/unified: no such command: 'configureFailPoint'
(make test fails on master with same result)
make test-race: same result as make test

With docker run -p 127.0.0.1:27017:27017 mongo

[matthewdale]

@jtagcat thanks for the PR and the proposed improvement! I agree that the CommandFailedEvent.Failure field should be an error instead of a string. However, changing that API would break our v1.x compatibility guarantee, so is not a change we can make currently.

I've created GODRIVER-2616 based on your proposed improvement and scheduled it for inclusion in the v2.0 Go Driver. For now I'm closing this PR. We will be welcoming PRs for the v2.0 Go Driver once that implementation is in-progress (please watch GODRIVER-1787 for updates)!

[jtagcat]

I subscribed to the Jira issue. I'm not sure whether Jira will send me notifications. I did not get any welcome e-mail, nor can I access any user settings to check notification method; all menus are white, persists with no blockers. If I'm needed, use e-mail or GitHub notifications.