Revert "Merge pull request #597 from blueboxgroup/backport-0.9.x-glance-store-check"

sensu_check prefix flag doesn't work as intended, it yields a sensu
config like this:
```
"command": "sudo . /root/stackrc;
GLANCE_IMAGE_DIR=/var/lib/glance/images
/etc/sensu/plugins/check-glance-store.py ",
```
Where we need to use sudo to access /root/stackrc and
/var/lib/glance/images but sudo can't execute bash builtin . and
check-glance-store.py isn't invoked as root.

This reverts commit 9f1297d121656683f87e6fda871305b02df4cd7e, reversing
changes made to 7ff1d5e0aa3257e37f35cf404ba15ad5763ae1a5.