Use node image to build javascript

We can use more than one builder image. Use the node image for
the javascript build so we can avoid spending time installing
node in the python builder image.

Change-Id: I19b18dd419b98119f75a8c3a9f3978f37f329e58

Dockerfile

@@ -13,6 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+FROM docker.io/library/node:14-buster as js-builder
+
+COPY web /tmp/src
+# Explicitly run the Javascript build
+RUN cd /tmp/src && yarn install -d && yarn build
+
 FROM docker.io/opendevorg/python-builder:3.8 as builder
 ENV DEBIAN_FRONTEND=noninteractive
 
@@ -25,14 +31,7 @@ ARG OPENSHIFT_URL=https://github.com/openshift/origin/releases/download/v3.11.0/
 ARG OPENSHIFT_SHA=4b0f07428ba854174c58d2e38287e5402964c9a9355f6c359d1242efd0990da3
 
 COPY . /tmp/src
-RUN /tmp/src/tools/install-js-tools.sh
-# Explicitly run the Javascript build.
-RUN cd /tmp/src \
-  && mkdir -p zuul/web/static \
-  && ln -sfn ../zuul/web/static web/build \
-  && cd /tmp/src/web \
-  && yarn install -d \
-  && yarn build
+COPY --from=js-builder /tmp/src/build /tmp/src/zuul/web/static
 RUN assemble
 
 # The wheel install method doesn't run the setup hooks as the source based