Allow persistent APKs updates using PM flags.

This is a different approach than
I346d772e1f4aed94f6faead3b6455efc4666b651, suggested during reviews.

Bug: 131046856
Test: marked the NetworkStack APK as persistent, verified that
  - adb install networkstack.apk fails
  - adb install --staged networkstack.apk succeds (after reboot)

Change-Id: I1facb24786431906a8056a50bff01745cebacf24