Convert "Empower" from state-based MFA to one-shot MFA
Summary: Ref T13382. Currently, the "Make Administrator" action in the web UI does state-based MFA. Convert it to one-shot MFA.
Test Plan: Empowered and unempowered a user from the web UI, got one-shot MFA'd. Empowered a user from the CLI, no MFA issues.
Maniphest Tasks: T13382
Differential Revision: https://secure.phabricator.com/D20729