Fix grouping of private flavors in launch instance

Flavor extra specs are currently cached once for all projects, which breaks
for private flavors where some projects see different flavors than others.

Cache flavor specs individually for each flavor to fix this.

Fixup for:
1f2f7fbac5d5596eb1eeee7071e15af01effeffd
I1b84a63fb91e14cf5f844b3aeb3a26e94390f142

Change-Id: Iaf84c55dfb04e6b2e896bd8ad4ec505ef0f172e3