Fix curl example refs in docs

The keystone developer docs index page had two links to the same
API examples page: "Service API Examples Using Curl" and
"Admin API Examples Using Curl". This is because the API examples
document had 2 top-level sections.

Partial-Bug: #1283943

Change-Id: I8204268aa482e59f9108d515b69e9c37a12a9e08
Merge "Fix curl example refs in docs"