Testruns are failing on OS X if real binary or new signed app bundle get specified (#183)

This will fix issue #183, and allows us to run a real binary and the new signed builds on OS X. @andreeamatei please review ASAP. Also can you please test this patch on Linux and Windows? I would kinda appreciate that.
We have to do some checks (see the upcoming signing checks on OS X), where we have to know which kind of path the user has specified. We can clean this up post 2.0.8.1 if necessary. For now I just combined the two methods to make it working and a bit easier to read.