Start tusd if it is not already running when performing `graceful`

Currently tusd is excluded from `graceful` in order to prevent any interruptions in uploading, but this also prevents it from being started if it's not already running, which is probably not what we want (and requires a manual start in the [tusd GTN tutorial](https://training.galaxyproject.org/training-material/topics/admin/tutorials/tus/tutorial.html).