Add slack channel when logging error.

[melchiormoulin]

Add the slack channel when logging error from slack.
#2176

[simonpasquier]

You need to sign your commit.

git amend -s
git push origin

[simonpasquier]

You can use github.com/pkg/errors to wrap the error which is a bit shorter:

       retry, err := n.retrier.Check(resp.StatusCode, resp.Body)
       err = errors.Wrap(err, fmt.Sprintf("channel %q", req.Channel))
       return retry, err

[melchiormoulin]

thanks for the tip

[melchiormoulin]

Is the test failed because of my commit ?
--- FAIL: TestReload (5.15s) acceptance.go:186: starting alertmanager cluster: starting alertmanager failed: timeout acceptance.go:177: Error sending SIGTERM to Alertmanager process: no such process

[simonpasquier]

This is a flake, I've retriggered the test.

[simonpasquier]

Thanks!