Use initializeNewLog rather than instantiate the UserLog

Summary:
Use initializeNewLog rather than instantiate the UserLog,
Closes T4912

Test Plan: Run install-certificate

Reviewers: #blessed_reviewers, btrahan

Reviewed By: #blessed_reviewers, btrahan

Subscribers: epriestley

Maniphest Tasks: T4912

Differential Revision: https://secure.phabricator.com/D8887