CVT: Mount spec should use File::expand_path for symmetry on Windows

Cause was device paths like /dev/sdb1 are mounted after File.expand_path is called on those paths -- the unit tests check config of mounted volumes looking for a path like /dev/sdba, but due to File.expand_path, the path has a "C:/" in it, which breaks the check. The fix was to call File.expand_path in the unit tests. Another option would be to stub File.expand_path to be a no-op, which begs then question of why it is being used in mount.rb...