Suppress warnings about transactional safety when running bloom-release

Currently when you run bloom-release the BLOOM_UNSAFE env variable is being set to speed up releases (since the repo is cloned and only pushed on success there is no need for cloning/pushing on a per command basis). Because of this you get messages like these:

```
Skipping transactional safety mechanism, be careful...
```

It should really only print these when this option is used directly by the user.