Fixing race condition in Galley Server.Close() (#11484)
Fixing race condition in Galley Server.Close() (#11484)

The issue was introduced by #11285

It causes a race with the startup of the gRPC server, which leads to a segfault.  From prow logs:

```
=== RUN TestServer_Basic 2019-02-01T20:33:05.867746Z	info	ControlZ available at 10.44.58.28:9876 2019-02-01T20:33:05.867968Z	info ControlZ terminated 2019-02-01T20:33:05.867987Z	info	runtime Stopping processor... 2019-02-01T20:33:05.868000Z	warn	runtime Processor has already stopped 2019-02-01T20:33:05.867798Z	info runtime	Starting processor... panic: runtime error: invalid memory address or nil pointer dereference [signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0x9e4bc8] goroutine 148 [running]: istio.io/istio/vendor/google.golang.org/grpc.(*Server).Serve(0xc42046d080, 0x0, 0x0, 0x0, 0x0) /home/prow/go/src/istio.io/istio/vendor/google.golang.org/grpc/server.go:522 +0x748 istio.io/istio/galley/pkg/server.(*Server).Run.func1(0xc4202d9490) /home/prow/go/src/istio.io/istio/galley/pkg/server/server.go:242 +0xfb created by istio.io/istio/galley/pkg/server.(*Server).Run /home/prow/go/src/istio.io/istio/galley/pkg/server/server.go:233 +0x5c FAIL	istio.io/istio/galley/pkg/server 0.383s
```
geeknoid/istio,istio/istio,smawson/istio,smawson/istio,geeknoid/istio,istio/istio,geeknoid/istio,istio/istio,geeknoid/istio,istio/istio,smawson/istio,geeknoid/istio,istio/istio,geeknoid/istio,smawson/istio,smawson/istio,smawson/istio