Fix docimpact_target project selection

I6c9a9f3f42b3a9eff33ca0522b9f23f058131433 introduced the ability to
map docimpact's to different launchpad projects but unfortunately
didn't select the correct project out of the YAML mapping.

Change-Id: If824aa429d4cf82eda474d9ff99b46d713b6af0f