Added error callback to spawn in spawnServer

Hey guys, 

I got this error recently when running some tests:
```
Error: spawn ENOENT
    at errnoException (child_process.js:1001:11)
    at Process.ChildProcess._handle.onexit (child_process.js:792:34)
```
It took me awhile to realize I didn't have `java` installed in my new dev machine. I thought I'd be cool to catch the `spawn` errors and give more details when a `no such file or directory` error is thrown. 

(I also removed an unnecessary `require`)