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