Improve testing for network blocking.

This simplifies the uidNetworkingBlocked method and makes it more
realistic by supporting more combinations of rules than just the
four used by this test.

Also support RULE_ALLOW_METERED, and add test coverage for it.

Test: test-only change
Change-Id: Id4f6c7f41429f3ae7841d3214b3e5e95ec591f85