try to fix unit test test_ProtoServer, test_TrainerOnePass

fix error: /paddle/paddle/.common_test_util.sh: line 97: netstat: command not found

Dockerfile

@@ -30,7 +30,8 @@ RUN apt-get update && \
     python-numpy python-matplotlib gcc g++ \
     automake locales clang-format-3.8 swig doxygen cmake  \
     liblapack-dev liblapacke-dev libboost-dev \
-    clang-3.8 llvm-3.8 libclang-3.8-dev && \
+    clang-3.8 llvm-3.8 libclang-3.8-dev \
+    net-tools && \
     apt-get clean -y
 
 # Install Go