Add installable property for prebuilt_apex

In case of shim apexes, we prebuilt all of them, but only need to
install v1 to a system partition.

Bug: 128677967
Test: manually checked that non-installable prebuilts don't end in /system
Change-Id: I112432abfd8f03cc7d7379ea3cab3f5491ace49c
Merged-In: I112432abfd8f03cc7d7379ea3cab3f5491ace49c
(cherry picked from commit dd53e8be)