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: Ibd78f23206ead96ce036fafb99a7bc394e6dd983
diff --git a/go/src/v.io/x/playground/testdata/src/ping/ping.go b/go/src/v.io/x/playground/testdata/src/ping/ping.go
index b942d96..abdb005 100644
--- a/go/src/v.io/x/playground/testdata/src/ping/ping.go
+++ b/go/src/v.io/x/playground/testdata/src/ping/ping.go
@@ -9,15 +9,15 @@
 import (
 	"fmt"
 
-	"v.io/v23"
 	"v.io/x/lib/vlog"
 	_ "v.io/x/ref/runtime/factories/generic"
+	"v.io/x/ref/test"
 
 	"pingpong"
 )
 
 func main() {
-	ctx, shutdown := v23.Init()
+	ctx, shutdown := test.V23Init()
 	defer shutdown()
 
 	s := pingpong.PingPongClient("pingpong")
diff --git a/go/src/v.io/x/playground/testdata/src/pong/pong.go b/go/src/v.io/x/playground/testdata/src/pong/pong.go
index 60bd5d9..b00e92c 100644
--- a/go/src/v.io/x/playground/testdata/src/pong/pong.go
+++ b/go/src/v.io/x/playground/testdata/src/pong/pong.go
@@ -16,6 +16,7 @@
 	"v.io/x/lib/vlog"
 	"v.io/x/ref/lib/signals"
 	_ "v.io/x/ref/runtime/factories/generic"
+	"v.io/x/ref/test"
 
 	"pingpong"
 )
@@ -29,7 +30,7 @@
 }
 
 func main() {
-	ctx, shutdown := v23.Init()
+	ctx, shutdown := test.V23Init()
 	defer shutdown()
 
 	serverPong := pingpong.PingPongServer(&pongd{})