We cannot use chdir to set the working directory on a per-isolate basis,
hence we need to specify absolute directories instead for this test to
work properly on multi-threaded runs.

R=yangguo@chromium.org
TEST=mjsunit/d8-os

Review URL: https://chromiumcodereview.appspot.com/9348051

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10639 ce2b1a6d-e550-0410-aec6-3dcde31c8c00