Create E2E test suite and consolidate tests

[jessepeterson]

Create a new E2E test suite. This supersedes the previous storage tests. However, importantly, most of this new test suite utilizes the actual HTTP handlers for more of an end-to-end test. This brought about a number of specific wins:

• We now test Bootstrap Tokens against all backends (was only the MySQL backend previously).
  • Fixed bugs in the file and PgSQL backends because of the tests!
• We have a unified device "emulation" (previously implemented per-backend).
• Consolidated shared test code into shared test package.
• As mentioned also testing the actual HTTP handlers (the "end-to-end" goal).
  • This includes testing the handlers, the service layer, and the storage backends.
  • This includes testing an API HTTP handler for e.g. enqueuing commands.
• Standardize on envvar-based test init for PgSQL backend (parity with MySQL backend)
• The protocol test package comes from newly refactored code in mdmb. Perhaps one day we can share more code.
• Along the way we also improved some handler creation protections with required arguments and/or better error handling.
• New test for token update tally accounting (which is tested across all backends).

[jessepeterson]

Fantastic. Caught another potential bug:

=== RUN   TestMySQL/e2e/bstoken
    bstoken.go:29: token for supposedly new device 66ADE930-5FDF-5EC4-8429-15640684C489 was not nil

[jessepeterson]

This is a good start. To avoid making perfect the enemy of progress here are some notes for improvements so this can merged:

• Test rigging/framework:
  • Merge device and enrollment packages. Main split right now is to support typed commands vs. raw streams.
  • Queue tests: maybe allow for specifying storage variations (for testing specific storage options?). This is in contrast to running the entire suite over a differently configured storage.
• Actual tests/things tested:
  • Push: Add tests for push systems. Probably requires mocking APNs.
  • Migrate certauth service tests. Probably needs work to allow misconfigured enrollments (i.e. changing out device identity certs to attempt to spoof). This may be low-level enough that it might want to be its own test package. migrate certauth tests to e2e #150
  • User channel tests (incl. UserAuthenticate/directory users).
  • Migration endpoint tests.