Bug 934690 - [B2G][FTU] Final screen of FTU does not have image

- this is a v1.2 branch fix
- update steps because depended bug 916262 is not uplifted to v1.2
Merge pull request #13680 from EragonJ/v1.2-bug-934690

Bug 934690 - [B2G][FTU] Final screen of FTU does not have image r=borjasalguero