Replace SIGHUP event with a custom event

[jasonmit]

This removes signalling across the process, since SIGHUP will terminate the process if nothing subscribes to this event (only on POSIX).

On non-Windows platforms, the default behavior of SIGHUP is to terminate Node.js, but once a listener has been installed its default behavior will be removed.

So, in the case of ember test nothing is subscribed so it terminates the process after the build completes and before the test run.

Unfortunately, counting listeners also does not work (reliably) since testem uses signal-exit which will make the count 1 when testing. And by default, signal-exit also terminates the process if no others are subscribed.

This change moves off process.emit in place of custom eventing on the addon instance.

Fixes #232

Review with https://github.com/ember-fastboot/ember-cli-fastboot/pull/234/files?w=1 since one file contained a mixture of tabs/spaces and my editor normalized them all to spaces.

/cc @rwjblue

[dustinfarris]

Confirm that ember test works for me now.

[rwjblue]

This looks good to me.

@tomdale - Can you also review?

[tomdale]

@rwjblue LGTM

[jasonmit]

Thanks @rwjblue @tomdale does this warrant a release since peoples builds are breaking?

[rwjblue]

Yes, definitely