Storm-webapp tests don't work on Windows

Several storm-webapp tests don't work on Windows because file paths like "/tmp" are used, and paths are sometimes constructed by String concatenation instead of using Path.resolve. The logviewer also doesn't seem to work on Windows, probably for the same reason.

I think there might be a few similar issues in other parts of the code, which I'd like to also fix as part of this.

I haven't checked whether this is a problem in 1.x, but it's likely.