add mako to multilang dockerimage

templates/tools/dockerfile/test/multilang_jessie_x64/Dockerfile.template

@@ -33,6 +33,9 @@
   RUN pip install coverage
   ENV PATH ~/.local/bin:$PATH
 
+  # Install Mako to generate files in grpc/grpc-node
+  RUN pip install Mako
+
   <%include file="../../run_tests_addons.include"/>
   # Define the default command.
   CMD ["bash"]

tools/dockerfile/test/multilang_jessie_x64/Dockerfile

@@ -152,6 +152,9 @@ RUN python3.4 -m pip install virtualenv
 RUN pip install coverage
 ENV PATH ~/.local/bin:$PATH
 
+# Install Mako to generate files in grpc/grpc-node
+RUN pip install Mako
+
 # Prepare ccache
 RUN ln -s /usr/bin/ccache /usr/local/bin/gcc
 RUN ln -s /usr/bin/ccache /usr/local/bin/g++