SSAID Migration to be Per App/User Unique Values.

SSAID is currently shared across all applications for each
user on the device, giving developers the ability to track
users across multiple applications. Using SSAID for tracking
is an abuse of the original intention of the SSAID and has
inherent privacy concerns.

This change will make the SSAID unique per application, per
user on a device. To not affect applications installed prior
to this change they will retain the legacy SSAID value until
uninstalled and reinstalled again.

Across subsequent installations the application will receive
the same SSAID as long as the package name and signature remain
consistent.

Tested manually the following cases:
  - App retains the legacy sssaid after OTA.
  - App gets a new ssaid upon post-OTA installation.
  - App retrieves same ssaid across post-OTA unistall/reinstalls.
  - Different Apps receive different ssaids.
  - Factory reset removes ssaid data and generates a different
    ssaid after App install.
  - System retains legacy ssaid.

Bug: 30979321
Test: CTS tests passed, Manual testing passed
Change-Id: I4acc190c14ec249e6365e05e7943148ed6f17f71