Installd: Change app image name computation

Refactor computation to take A/B OTAs into account.

Fix a const issue.

Bug: 25612095
Change-Id: I5cf79def532d1eeec4b35bb80014376959083a83
(cherry picked from commit d01a02ce6980de0024333b4673cff9a77be629cf)
2 files changed