Minimize nginx container using the os-core container.

Convert nginx container to be based on the minimal os-core
container, using a multistage build technique to add additional
Clear Linux content.

Signed-off-by: Rusty Lynch<rusty.lynch@intel.com>

nginx/Dockerfile

@@ -1,15 +1,30 @@
-FROM clearlinux:latest
-MAINTAINER bin.yang@intel.com
-
-ARG swupd_args
+FROM clearlinux:latest AS builder
 
+# Move to latest Clear Linux release to ensure
+# that the swupd command line arguments are
+# correct
 RUN swupd update --no-boot-update $swupd_args
 
+# Grab os-release info from the minimal base image so
+# that the new content matches the exact OS version
+COPY --from=clearlinux/os-core:latest /usr/lib/os-release /
+
+# Install additional content in a target directory
+# using the os version from the minimal base
+RUN source /os-release && \
+    mkdir /install_root \
+    && swupd os-install -V ${VERSION_ID} \
+    --path /install_root --statedir /swupd-state \
+    --bundles=nginx --no-scripts \
+    && rm -rf /install_root/var/lib/swupd/*
+
+FROM clearlinux/os-core:latest
+MAINTAINER bin.yang@intel.com
+
+COPY --from=builder /install_root /
 COPY default.conf /etc/nginx/conf.d/default.conf
 
-RUN swupd bundle-add nginx $swupd_args && \
-    rm -rf /var/lib/swupd/* && \
-    mkdir -p /var/log/nginx && \
+RUN mkdir -p /var/log/nginx && \
     # forward request and error logs to docker log collector
     ln -sf /dev/stdout /var/log/nginx/access.log && \
     ln -sf /dev/stderr /var/log/nginx/error.log && \