Removing specs from finagle/finagle-native test.

Going along with the corresponding issue https://github.com/twitter/finagle/issues/290 and my other PR on the subject https://github.com/twitter/finagle/pull/292


instead of calling an init method, the style we typically use is to either make a Context class that we construct and import members from, or make a wrapper method that can do the construction for us.  this means that we don't have to worry about sharing objects.

For example:

```scala
class Ctx {
  val input = ...
}

val ctx = new Ctx()
import ctx._
```

or

```scala
def exec(fn: Input => Unit) {
...
}

exec { input =>

}
```