This test deleted its working directory and then tried to run several
shell commands which caused a failure on nfs.

Changes:
-TEST_DIR is only removed at the very end of the test
-the working directory is changed to /tmp at the beginning so that
 every iteration (when running with --stress-opt) has a valid working directory

BUG=
TEST=

Review URL: http://codereview.chromium.org/8936004
Patch from Daniel Kalmar <kalmard@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10240 ce2b1a6d-e550-0410-aec6-3dcde31c8c00