Fix errors in used_limits extension

Fixes bug #1062049

There was a typo mapping the security groups resource to floating IPs.

Key pairs don't work with the extension because of bug #1089877.

(cherry picked from commit 6c9d9ab)

Change-Id: Ifd694b21fef1dc95e67c07dcef0cd6ea3daa8d53
Merge "Fix errors in used_limits extension" into stable/folsom