bug 1468491: Update to node 8, update packages

Update from node 6.x to 8.x, copying the installation from the official
node package. This drops the xz-utils package, adds a node user, and one
more signing key.

Minimally update the node.js packages:

* fibers 1.0.15 → 2.0.2: Drop node v4, fix v6 and v8

Drop csslint, which appears to be unused.

docker/images/kuma_base/Dockerfile

@@ -1,7 +1,7 @@
 FROM python:2.7-slim
 
 # Set the environment variables
-ENV NODE_VERSION=6.14.2 \
+ENV NODE_VERSION=8.11.3 \
     # extra python env
     PYTHONDONTWRITEBYTECODE=1 \
     PYTHONUNBUFFERED=1 \
@@ -21,7 +21,6 @@ RUN set -x \
     && apt-get update \
     && apt-get install -y --no-install-recommends \
         curl \
-        xz-utils \
         gpg \
         dirmngr \
         libsasl2-modules \
@@ -39,11 +38,15 @@ RUN set -x \
     && rm -rf /var/lib/apt/lists/*
 
 # ----------------------------------------------------------------------------
-# add node.js 6.x, copied from:
-#     https://github.com/nodejs/docker-node/blob/master/6/stretch/Dockerfile
-# but with package updates and version definitions moved above
+# add node.js 8.x, copied from:
+#     https://github.com/nodejs/docker-node/blob/master/8/stretch/Dockerfile
+# but with package updates and version definitions moved above, and the node
+# user gets uid/gid 1001 rather than 1000.
 # ----------------------------------------------------------------------------
 
+RUN groupadd --gid 1001 node \
+  && useradd --uid 1001 --gid node --shell /bin/bash --create-home node
+
 RUN set -ex \
   && for key in \
     94AE36675C464D64BAFA68DD7434390BDBE9B9C5 \
@@ -54,6 +57,7 @@ RUN set -ex \
     B9AE9905FFD7803F25714661B63B535A4C206CA9 \
     56730D5401028683275BD23C23EFEFE93C4CFFFE \
     77984A986EBC2AA786BC0F66B01FBB92821C587A \
+    8FCCA13FEF1D0C2E91008E09770F7A9A5AE15600 \
   ; do \
     gpg --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys "$key" || \
     gpg --keyserver hkp://ipv4.pool.sks-keyservers.net --recv-keys "$key" || \
@@ -85,9 +89,8 @@ RUN adduser --uid 1000 --disabled-password --gecos '' --no-create-home kuma
 WORKDIR /app
 EXPOSE 8000
 
-RUN npm install -g \
-        fibers@1.0.15 \
-        csslint@0.10.0 \
+RUN npm install --unsafe-perm -g \
+        fibers@2.0.2 \
         jshint@2.7.0 \
         node-sass@4.3.0 \
         uglify-js@2.4.13 \