When deploying phabricator with scap3, I ran into this issue:

Phabricator has several files / directories / permissions which are managed by puppet.

The solution that seems most straightforward is to have a hook that calls puppet after the promote stage, but it needs to run before restart.

By making restart into a separate deployment stage we can call hooks right before restart, which is not possible currently.

The other benefit is that we could manually run a restart without running any other stages of a deployment, which is going to be needed for Scap (Scap3-MediaWiki-MVP)