Gather Weave Net plugin and proxy info from report

Instead of using Docker, because after Weave Net 2.0 there are no proxy nor
plugin containers.

This has the drawback of not detecting the plugin/proxy in systems running
Weave Net < 2.0 , but I think we can live with it.

test/weave/mock.go

@@ -15,6 +15,8 @@ const (
 	MockContainerMAC       = "d6:f2:5a:12:36:a8"
 	MockContainerIP        = "10.0.0.123"
 	MockHostname           = "hostname.weave.local"
+	MockProxyAddress       = "unix:///foo/bar/weave.sock"
+	MockDriverName         = "weave_mock"
 )
 
 // MockClient is a mock version of weave.Client
@@ -54,6 +56,12 @@ func (MockClient) Status() (weave.Status, error) {
 				{Size: 0, IsKnownPeer: false},
 			},
 		},
+		Proxy: &weave.Proxy{
+			Addresses: []string{MockProxyAddress},
+		},
+		Plugin: &weave.Plugin{
+			DriverName: MockDriverName,
+		},
 	}, nil
 }