Look for MSTest in VS2015 location

[brodyberg]

I noticed while attempting to use the MSTest that it wouldn't find it if I was using VS 2015. The proposed fix adds the VS 2015 path, in the order demonstrated by the existing array, which has newer versions of VS closer to the beginning.

I got a very cryptic error with this issue, not fixed with this PR:

System.Exception: Start of process  failed. Cannot start process because a file name has not been provided.

I also noticed that if FAKE can't find MSTest with a value from the mstestPaths array it supplies a path of "". Is that because it hopes to luck-out and find MSTest on the %PATH%?

While we are on the subject of paths to VS assets, would it be a better idea if all path computations regarding the VS location were done in one place so we don't have to (presumably) fix this in each case where we create a mstestPaths analog? Say for something like gacutil (just thinking off the top of my head).

Thanks,

Brody

[forki]

yes I'm open for backwards-compatible improvements.