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 CtsNetTestCasesLatestSdk:android.net.NetworkProviderTest
Change-Id: If7bfc7fae503e3497c37754697d0b148ff4cab3b