Set user on auxiliary fields before validating them on template workflow

Summary: Some fields need this data in some circumstances in order to validate

• see D1153.

Test Plan: Ran "arc diff" against local, no longer got an exception for access
of this field from the 'Reviewers' validator.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, btrahan

Differential Revision: 1160