Fix worlddump call

Change I8db9dc99da8bb486a07d7ead77031e1c0b419857 modified failure
paths to call worlddump.py, but this instance is looking in the wrong
path; e.g.

---
2014-12-02 20:29:21.371 | The following services are not running after upgrade:  swift-proxy-server
2014-12-02 20:29:21.372 | /opt/stack/new/grenade/check-sanity: line 117: /opt/stack/new/grenade/tools/worlddump.py: No such file or directory
2014-12-02 20:29:21.373 | + die 377 'Failure in check-sanity'
---

Also, ${LOGDIR} isn't defined here, so output to the devstack screen
log dir

[1] http://logs.openstack.org/28/136328/2/check/check-grenade-dsvm/0328b64/logs/grenade.sh.txt.gz

Change-Id: I18d96a47469d34e0df51f0a6b9b9e16925a3c3df
(cherry picked from commit 12c6b73261471a57eefe116114fb1c8fe23ca04d)