Restructure GetExecutablePath test
Restructure GetExecutablePath test

The logic depending on `RunningTests` was added in 5063857b, but doesn't
make sense to me now. If we're running this test, we should always be
running tests!

I also rearranged and simplified some of the assertions for better
diagnosability.

Microsoft/msbuild,Microsoft/msbuild,jeffkl/msbuild,mono/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,mono/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,Microsoft/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,chipitsine/msbuild,jeffkl/msbuild,chipitsine/msbuild,rainersigwald/msbuild,mono/msbuild,chipitsine/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,jeffkl/msbuild,mono/msbuild,jeffkl/msbuild,cdmihai/msbuild,chipitsine/msbuild,AndyGerlicher/msbuild,AndyGerlicher/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,Microsoft/msbuild,rainersigwald/msbuild