v.io: use test.V23Init instead of v23.Init in test code

test.V23Init creates a context that's suitable for tests, including a
test blessing and no prod mounttable root. Using test.V23Init everywhere
in tests gives us a choke-point for adding test-specific configuration
of the runtime and context.

Change-Id: I88fe7713b1aa79807e5f51888ed479d6d1d6e041
diff --git a/clients/shell/go/src/v.io/x/chat/channel_test.go b/clients/shell/go/src/v.io/x/chat/channel_test.go
index 9800320..366b6d7 100644
--- a/clients/shell/go/src/v.io/x/chat/channel_test.go
+++ b/clients/shell/go/src/v.io/x/chat/channel_test.go
@@ -15,12 +15,13 @@
 	"v.io/x/lib/gosh"
 	"v.io/x/ref/lib/signals"
 	"v.io/x/ref/services/mounttable/mounttablelib"
+	"v.io/x/ref/test"
 	"v.io/x/ref/test/v23test"
 )
 
 // TODO(sadovsky): Switch to using v23test.Shell.StartRootMountTable.
 var rootMT = gosh.RegisterFunc("rootMT", func() error {
-	ctx, shutdown := v23.Init()
+	ctx, shutdown := test.V23Init()
 	defer shutdown()
 
 	mt, err := mounttablelib.NewMountTableDispatcher(ctx, "", "", "mounttable")