Minor tidying of `ArcanistUpgradeWorkflow`
Minor tidying of `ArcanistUpgradeWorkflow`

Summary: Self-explanatory.

Test Plan: Eyeball it.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11554

julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist