Move infrastructure tests up one directory.

Summary: Sometimes, the `PhutilInfrastructureTestCase` //would// fail, but we don't run it with `arc unit` because of the directory structure. See D9556 for an example.

Test Plan: Ran `arc unit --everything` and verified that `PhutilInfrastructureTestCase` was executed.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9557