Fix multiple instances and no method 'async' bug

closes #28
closes #30
- added stopdone to wait for server to stop
- renamed done to startdone
- added conditional for `grunt.task.current.async()`
- added testsequence which is able to reproduce the bug without my
changes to server.js
- added `express:defaults` without `express:defaults:stop` at the end
of the file to reproduce missing 'async'