rocon_msgs: 0.6.8-0 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `rocon_msgs` to `0.6.8-0`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.1`
- previous version for package: `0.6.7-1`

## scheduler_msgs

- No changes

## rocon_msgs

```
* adding interaction messages and updated scheduler_msgs.
* Contributors: Daniel Stonier
```

## rocon_std_msgs

```
* some string type messages and service pairs.
* Contributors: Daniel Stonier
```