[tests] Fix tests which rely on temp dir location being a real dir

[tests] Fix tests which rely on temp dir location being a real dir

Android M (that's where I ran into it) makes the path returned by
Path.GetTempPath () a symlink to the real directory used for temporary
files. When the tests change the directory the symlink is followed and
subsequent reads of the current directory name will return the real dir
name which doesn't match what was constructed using the value returned by
GetTempPath ()