fix compilation error because of the following grpc change.
fix compilation error because of the following grpc change.

"author iamqizhao <toqizhao@gmail.com> Mon Apr 18 16:18:34 2016 -0700"

masato25/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend