Logic to confirm permissions on install sessions.

When an app without INSTALL permission attempts to commit a session,
we involve user to confirm permissions.  We currently point at the
base APK, which defines all permissions for an app, handling the case
where a session may only be adding splits.

Add failure codes to represent rejection.  Fix bug by ignoring stages
during initial boot scan.

Bug: 16515814
Change-Id: I702bb72445216817bcc62b79c83980c1c2bb0120