CUMULUS-337 Rely on NODE_ENV instead of TEST for detecting tests

[marchuffnagle]

Summary: Rely on ava's NODE_ENV=test environment variable to detect a test run

Addresses CUMULUS-337: Update test-specific code to rely on NODE_ENV instead of TEST env vars

Changes

• Update ava to 0.23.0, which added the NODE_ENV variable
• Add an inTestMode function to the test-utils module
• Move the createQueue function from common/test-utils to common/aws to resolve a circular dependency that this change introduced

Test Plan

• Unit tests
• Run ./bin/eslint-ratchet and verify that eslint errors have not increased
  • Commit .eslint-ratchet-high-water-mark if the score has improved