rose suite-run (gtk): fix RuntimeError for Queues

When running `rose suite-run` through `rose edit` or `rosie go`, the suite run
process currently stalls with:
```
RuntimeError: Queue objects should only be shared between processes through inheritance
```
for new or newly-named non-trivial suites.

This can be traced back to `77c074ffe`, which introduced a lot more file events
that all go into the `Queue` for the special GUI event handler's stdout stream (
`ReporterContextQueue`).

Using a `multiprocessing.Manager` to generate the `Queue` seems to implement
a more sharing-friendly kind of Queue, which prevents the error from
re-occurring.

@matthewrmshin, please review.