Add support for testemMiddleware to ember test --server

Pass options to invokeTestem

Move testemOptions into separate function
... reference this.testum inside invokeTestem()

Remove unused callback argument
Merge pull request #2462 from AdamFerguson/test-server-middleware

Add support for testemMiddleware to ember test --server
Use project.root as process.cwd(), so files aren't generated in wrong places
Merge pull request #2499 from marcioj/mj-issue-2364

Use project.root as process.cwd(), so files aren't generated in wrong pl...