Separate integration tests

This pull request separates integration tests into a `integration/` directory. Integration tests are any tests which require running an actual docker server, starting containers, downloading test images etc.

- [x] Keep only unit tests in the main docker package
- [x] Integration tests should pass
- [x] Move TestMount to integration test
- [x] Refactor some tests to use engine
- ~~[ ] Call integration tests automatically from make.sh in a separate bundle~~ *this will be done in a separate pull request*
- [x] Move non-unit iptables tests into integration/
- [x] Move non-unit auth tests into integration/
- [x] Uncomment tests in api_test.go