Conditional OuterLoop attribute is needed for expressing that a test should go to outer loop on certain platforms only

[lukas-lansky]

Runtime ran into a situation (issue, pr) where a certain class of tests should be ran in the outer loop context only on certain platforms. Elsewhere, it should be executed in the inner loop. Some cross-over between OuterLoop and SkipOnPlatform is needed for this usecase.

cc @riarenas