[packager] Working directory for Mac OS bundles is always home directory, not app directory

For apps bundled with the packager, windows and linux each change the working dir to the root directory that contains the resources specified by the bundler, i.e. all the jars. But on mac the working directory is always the user (or container's) home directory. This should be the same functional directory it is in Win and Linux, i.e. $PACKAGEDIR