Set up and tear down test network in TestNetworkRunnable

Allow test caller to construct a TestNetworkRunnable to run a
test with a test network.

This is a preparation for adding tests to verify kernel
implementation of IPsec algorithms.

Bug: 171083832
Test: atest Ikev2VpnTest
Original-Change: https://android-review.googlesource.com/1503692
Merged-In: I0e08a6ea299e6ad94d69806a2d76fa155653b62a
Change-Id: I0e08a6ea299e6ad94d69806a2d76fa155653b62a
2 files changed