Move NG-UI Dockerfile to use a build stage

Change-Id: I23685d6fea5a61048b367981468a91fcd8de0473
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>

docker/NG-UI/Dockerfile

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM ubuntu:18.04
+FROM ubuntu:18.04 AS BUILD
 
 RUN DEBIAN_FRONTEND=noninteractive apt-get --yes update && \
     DEBIAN_FRONTEND=noninteractive apt-get --yes install \
@@ -40,13 +40,22 @@ RUN npm install
 
 # Building app.
 RUN npm run build
-RUN cp /usr/share/osm-ngui/nginx/nginx.conf /etc/nginx/sites-available/default
+
+FROM ubuntu:18.04 AS FINAL
+
+RUN DEBIAN_FRONTEND=noninteractive apt-get --yes update && \
+    DEBIAN_FRONTEND=noninteractive apt-get --yes install \
+    nginx=1.14.* && \
+    rm -rf /var/lib/apt/lists/*
 
 # Removing the Nginx default page.
 RUN rm -rf /usr/share/nginx/html/*
 
+# Copying Nginx configuration
+COPY --from=BUILD /usr/share/osm-ngui/nginx/nginx.conf /etc/nginx/sites-available/default
+
 # Copying angular build to Nginx default page.
-RUN cp -r /usr/share/osm-ngui/dist/osm/* /usr/share/nginx/html
+COPY --from=BUILD /usr/share/osm-ngui/dist/osm /usr/share/nginx/html
 
 EXPOSE 80