Put back the stronger variable replacement

Summary: This puts back the stronger variable replacement that was missed the last update to D7519.

Test Plan: Re-ran a remote build that had variables in the command and everything worked as expected.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T1049

Differential Revision: https://secure.phabricator.com/D7539