TT#22402 Switch ngcp-csc Dockerfile to Debian stretch

+ TT#22410 Fix typo in Dockerfile 'Instructions for usage'

+ We have to bump Java 8 here as Java 7 is not available in Stretch:
> Package 'openjdk-7-jre-headless' has no installation candidate

Change-Id: I840a8ef9b5b7557bfff36f9928d822e6ddd61229

t/Dockerfile

@@ -1,11 +1,11 @@
-# DOCKER_NAME=ngcp-csc-jessie
-FROM docker.mgm.sipwise.com/sipwise-jessie:latest
+# DOCKER_NAME=ngcp-csc-stretch
+FROM docker.mgm.sipwise.com/sipwise-stretch:latest
 
 # Important! Update this no-op ENV variable when this Dockerfile
 # is updated with the current date. It will force refresh of all
 # of the base images and things like `apt-get update` won't be using
 # old cached versions when the Dockerfile is built.
-ENV REFRESHED_AT 2017-06-30
+ENV REFRESHED_AT 2017-09-25
 
 # files that get-code generates
 COPY t/sources.list.d/builddeps.list /etc/apt/sources.list.d/
@@ -17,7 +17,7 @@ RUN apt-get update && apt-get install --assume-yes \
         devscripts \
         libgconf-2-4 \
         nodejs \
-        openjdk-7-jre-headless \
+        openjdk-8-jre-headless \
         sencha-cmd \
         unzip \
         xvfb
@@ -52,17 +52,16 @@ WORKDIR /code
 #
 # you need to put the proper NGCP sources at t/sources.list.d/builddeps.list
 # for instance, trunk:
-# echo "deb https://deb.sipwise.com/autobuild/ release-trunk-jessie main" > /
-#  t/sources.list.d/builddeps.list
+# echo "deb https://deb.sipwise.com/autobuild/ release-trunk-stretch main" > t/sources.list.d/builddeps.list
 #
 # NOTE: run the following commands from root folder of git repository:
-# % docker build --tag="ngcp-csc-jessie" -f ./t/Dockerfile .
-# % docker run --rm -i -t -v $(pwd):/code:ro -v /results ngcp-csc-jessie:latest bash
+# % docker build --tag="ngcp-csc-stretch" -f ./t/Dockerfile .
+# % docker run --rm -i -t -v $(pwd):/code:ro -v /results ngcp-csc-stretch:latest bash
 #
 # Use the existing docker image:
-# % docker pull docker.mgm.sipwise.com/ngcp-csc-jessie
+# % docker pull docker.mgm.sipwise.com/ngcp-csc-stretch
 # NOTE: run the following command from root folder of git repository:
-# % docker run --rm -i -t -v $(pwd):/code:ro -v /results docker.mgm.sipwise.com/ngcp-csc-jessie:latest bash
+# % docker run --rm -i -t -v $(pwd):/code:ro -v /results docker.mgm.sipwise.com/ngcp-csc-stretch:latest bash
 #
 # Inside docker:
 #   cd /code && ./t/testrunner