1. Test NetworkCallbacks as well as CONNECTIVITY_ACTION, since
we are moving away from CONNECTIVITY_ACTION.
2. Use the Network objects we get back to test
Network#getSocketFactory().
3. Check that TCP connections are closed with ECONNABORTED when
a network disconnects.
Bug: 28251576
Change-Id: I41a438b82ef9251e52866332f3445f1bf876e04f