This contains a squash of two changes

>>>>>>>>>>>>>>>>>>>>>>
aosp/1284588
Adjust permission of NetworkProvider related API

- Allow an app holds NETWORK_SETTINGS to acess registerNetworkProvier()
  and unregisterNetworkProvider().
- To access declareNetworkRequestUnfulfillable(), allow an app holds
  MANAGE_TEST_NETWORKS to declare a unfulfillable request that contains
  TRANSPORT_TEST transport.

This makes easier to write cts to test.
>>>>>>>>>>>>>>>>>>>>>>
aosp/1285957
Add cts test for NetworkProvider

It will skip whole tests on Q device since NetworkProvider class
is introduced in R.

Result on Q device would be:
[1/1] android.net.NetworkProviderTest#skippedClassForDevSdkMismatch: IGNORED (3ms)
>>>>>>>>>>>>>>>>>>>>>>
Bug: 153614605
Bug: 153613690
Bug: 153612373
Test: atest FrameworksNetTests
      atest CtsNetTestCases:android.net.NetworkProviderTest
Test: atest CtsNetTestCasesLatestSdk:android.net.NetworkProviderTest
Change-Id: Ib6f42b8f0e94e8c2715a030587e065864edff25b
Merged-In: Ic9809e731aa811a51c2f82d189372169d99a5ed9
Merged-In: If7bfc7fae503e3497c37754697d0b148ff4cab3b
(cherry picked from commit 10138d42)