Fix broken link to object storage admin guide

As noted in the report, this was linking to the object storage admin
guide as if it was within the compute admin guide. An extra .. should
fix this.

**Needs backport to stable/grizzly

fixes bug 1188523

Change-Id: I22d8a3c3810557c9d8cb6fc998c53983736fd14c
Merge "Fix broken link to object storage admin guide"