various fixes (#1267)

* logger: remove Panic log level

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* server/grpc: add missing Unlock in Subscribe error

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* server: minor code change

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* server/grpc: extend test suite with pub/sub testing

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* server/grpc: fix invalid check and allow subscriber error to be returned

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* server/grpc: add pubsub tests

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

* client/grpc: check for nil req/rsp

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

client/grpc/grpc.go

@@ -383,6 +383,11 @@ func (g *grpcClient) NewRequest(service, method string, req interface{}, reqOpts
 }
 
 func (g *grpcClient) Call(ctx context.Context, req client.Request, rsp interface{}, opts ...client.CallOption) error {
+	if req == nil {
+		return errors.InternalServerError("go.micro.client", "req is nil")
+	} else if rsp == nil {
+		return errors.InternalServerError("go.micro.client", "rsp is nil")
+	}
 	// make a copy of call opts
 	callOpts := g.opts.CallOptions
 	for _, opt := range opts {