Enable background restrictions

Apps that target O+ are always subject to background restrictions.
Legacy apps' background restriction is subject to the OP_RUN_IN_BACKGROUND
app op.

Apps with these properties are exempted from background restrictions:
  - persistent process
  - currently on the idle battery whitelist
  - global whitelist for things like bluetooth services

Bug 30953212

Change-Id: Ib444829a2d222125f64ff19e8218823fa78373f9