GitLab

Bumps [go.uber.org/multierr](https://github.com/uber-go/multierr) from 1.4.0 to 1.5.0.
- [Release notes](https://github.com/uber-go/multierr/releases)
- [Changelog](https://github.com/uber-go/multierr/blob/master/CHANGELOG.md)
- [Commits](https://github.com/uber-go/multierr/compare/v1.4.0...v1.5.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Instead of giving up when a single datastore fails, operate on all datastores
first. That way:

* If one datastore doesn't support disk usage, we can at least return our best
  estimate for the ones that do.
* If one datastore fails to sync, we won't fail to sync the others.
* If one datastore refuses to close, we'll close the others.

Etc.

Also:

* Drop xerrors. We already need go 1.13 elsewhere.
* Use uber's multierr. It's much simpler than hashicorps (and is already a
  dependency through zap, fx, etc.).

Now we just need a common place to put:

func IsNotFound(e error) bool {
  for e != nil {
    if ne, ok := e.(interface { NotFound() bool }); ok {
      return ne.NotFound()
    }
    if ue, ok := e.(interface { Unwrap() error }); ok {
      e = ue.Unwrap()
    } else {
      return false
    }
  }
  return false
}