logging: update tracing and tracing-subscriber

Updating to the latest versions of the `tracing` and
`tracing-subscriber` crates picks up a few changes that might be
relevant to us:

- tokio-rs/tracing#333: Fix an issue where filtering directives could
  sometimes be ignored
- tokio-rs/tracing#344: Fix for filters not applying to events generated
  from `log` records
- tokio-rs/tracing#346: Dependencies using `tracing`'s `log` back-compat
  alongside the `log` record to `tracing` event conversion layer will no
  longer result in duplicate events

Additionally, `tracing-subscriber` 0.1.2 removed some dependencies that
were previously on by default, and feature flagged others; I've tweaked
the feature flags that we enable so we now have fewer transitive deps in
our lockfile :D

Signed-off-by: Eliza Weisman <eliza@buoyant.io>