Return :preferences if device cannot be detected

When the device target cannot be found, this method was
raising an error.  Unknown targets (devices or sims) should
be detected either before or after this method.
Merge pull request #521 from calabash/feature/push-device-not-connected-problem-up-the-stack

Return :preferences if device cannot be detected
Fix commit 6f68b8a - copy and paste error
Use RunLoop::SimControl to quit/launch sims
SimLauncher quit_sim is not ready for Xcode 6