Fix missing onLost NetworkCallbacks when network loses capability

If a network no longer satisfies a NetworkRequest, send the onLost
NetworkCallback.  If it was a real request (not listen) then update
the NetworkFactories.

To test this change I created a little infrastructure to fake
different Internet connectivity probe results during tests.  This
allowed me to rewrite some of ConnectivityServiceTest's logic for
validating networks.  This brought to light a couple issues that
I had to address to keep tests passing:
1. testUnlingeringDoesNotValidate was relying on a bad side-effect
   of my old method of ConnectivityServiceTest's logic for
   validating networks, so I rewrote the test.
2. ConnectivityService was not sending out NetworkCallbacks for
   WiFi when Cellular was validated.  I'm including a fix for this
   in this CL also.

Bug:22220234
Change-Id: I29314f38189817f8b2561a213c4f9e8522696663

core/java/android/net/NetworkCapabilities.java

@@ -626,6 +626,7 @@ public final class NetworkCapabilities implements Parcelable {
                 case NET_CAPABILITY_TRUSTED:        capabilities += "TRUSTED"; break;
                 case NET_CAPABILITY_NOT_VPN:        capabilities += "NOT_VPN"; break;
                 case NET_CAPABILITY_VALIDATED:      capabilities += "VALIDATED"; break;
+                case NET_CAPABILITY_CAPTIVE_PORTAL: capabilities += "CAPTIVE_PORTAL"; break;
             }
             if (++i < types.length) capabilities += "&";
         }