Add ConnectivityServiceIntegrationTest

This test exercises the Connectivity <-> NetworkMonitor integration.
This CL only contains a simple test (network validates), but more
generally it sets up a test package that contains both services.jar
classes and NetworkStack classes, and runs NetworkStack components in
another process (using TestNetworkStackService).

ConnectivityServiceIntegrationTest runs in the test process and binds to
TestNetworkStackService to obtain TestNetworkStackConnector and to
NetworkStackInstrumentationService to obtain
NetworkStackInstrumentationConnector. That last connector allows the
test to mock NetworkMonitor HTTP Requests.

Test: atest FrameworksNetIntegrationTests
Change-Id: Ieca18e273609044cf6b1870d2f0dba33ca7b38d3