QmlEngine: Move setup logic from setupInferior to setupEngine

This is more in line with e.g. the gdb engine, which also emits
requestRemoteSetup in setupEngine().

Change-Id: I1c2a4c56d6f190a3043ea8a18d2bb28c9d340826
Reviewed-by: Aurindam Jana <aurindam.jana@nokia.com>