Use V8 branch in Vaadin 8 related builds

[pleku]

Framework 8.7: (latest maintenance)

• [x] Release build
• [x] Snapshots build ?
• [x] Test build ? Framework master (8.8)
• [x] Release build
• [x] Snapshots build ?
• [x] Test build ?

[ZheSun88]

Archetype has been used only Framework release build configurations neither in snapshot nor test.

corresponding VCS root has been changed to use V8 instead of master.