Use lazy initialization for the default grpc client

This avoids using a public global variable. It allows us to initialize
the default client a bit later (outside of init()). That way we can e.g.
properly initialize the in-memory registry.

services/search/pkg/command/index.go

@@ -37,7 +37,7 @@ func Index(cfg *config.Config) *cli.Command {
 			return parser.ParseConfig(cfg)
 		},
 		Action: func(c *cli.Context) error {
-			client := searchsvc.NewSearchProviderService("com.owncloud.api.search", grpc.DefaultClient)
+			client := searchsvc.NewSearchProviderService("com.owncloud.api.search", grpc.DefaultClient())
 			_, err := client.IndexSpace(context.Background(), &searchsvc.IndexSpaceRequest{
 				SpaceId: c.String("space"),
 				UserId:  c.String("user"),