Set tmp and home dir env to within the workspace

[vmx]

Windows worker often run out of disk space. @victorbjelkholm mentioned that one issue is that tests write into the tmp and home directories and don't clean up properly after themselves.

One way of solving this would be to re-define the TEMP/TMP and HOME/HOMEPATH/USERPROFILE environment variables to be within the workspace, so that the workspace cleanup would also cleanup those files.

There's a nice list on env variables per platform on Wikipedia.