Move the OpenHelperManager.release method in setDatabaseHelperRef()

Based on an advices with @WonderCsabo:
The whole map is not needed. Just add the release method in setDatabaseHelperRef which is already implemented to be called only once per helper type.
Remove an unnecessary judgment condition in onDestroy method.

Based on an advice with @WonderCsabo:
Is it possible that the databaseHelper is null at this point?
Oftentimes, not.
Create another test(OrmLiteOnDestroyActivity) for a more cleaner test.

Based on an advice with @WonderCsabo:
Maybe you should create another test Activity for a more cleaner test?
On that, you can check just the helper was closed or not.
Use Robolectric's ActivityController instead of calling onDestroy directly

Based on an advice with @WonderCsabo:
Please use Robolectric's ActivityController instead ot calling lifecycle method directly.