syncbase: Prevent returned errors from leaking existence.

All client-to-Syncbase methods (db/cx/row, syncgroup manager, blob, cr)
have been sanitized to return ErrNoExistOrNoAccess when the caller has
no permission to know about the existence of an object.

GetDeltas and JoinSyncgroupAtAdmin have also been sanitized (GetDeltas
returns ErrDbOffline instead). PublishSyncgroup cannot be sanitized
until authentication is added to it.

Tests in subsequent CL.

MultiPart: 3/3
Change-Id: I54df90a973edabfa8e31e12000e5ff9115bd699c
diff --git a/go/src/v.io/x/sensorlog/internal/sbutil/syncbase_test.go b/go/src/v.io/x/sensorlog/internal/sbutil/syncbase_test.go
index 1f51e24..e6aabb3 100644
--- a/go/src/v.io/x/sensorlog/internal/sbutil/syncbase_test.go
+++ b/go/src/v.io/x/sensorlog/internal/sbutil/syncbase_test.go
@@ -25,9 +25,9 @@
 	defer cleanup()
 	ctxGuest := sbtu.NewCtx(ctxOwner, rootPrincipal, "u:two")
 
-	// Try to open (create) db as guest, fail with ErrNoAccess.
-	if _, err := sbutil.CreateOrOpenDB(ctxGuest, sbName, sbmodel.MasterCollections); verror.ErrorID(err) != verror.ErrNoAccess.ID {
-		t.Errorf("CreateOrOpenDB should have failed with ErrNoAccess, got error: %v", err)
+	// Try to open (create) db as guest, fail with ErrNoExistOrNoAccess.
+	if _, err := sbutil.CreateOrOpenDB(ctxGuest, sbName, sbmodel.MasterCollections); verror.ErrorID(err) != verror.ErrNoExistOrNoAccess.ID {
+		t.Errorf("CreateOrOpenDB should have failed with ErrNoExistOrNoAccess, got error: %v", err)
 	}
 	// Open (create) db as owner.
 	dbOwner, err := sbutil.CreateOrOpenDB(ctxOwner, sbName, sbmodel.MasterCollections)