chore(dockerfile): various Dockerfile cleanups (spinnaker#1304)

* chore(dockerfile): delete the (unused) java8 dockerfiles

* chore(dockerfile): replace deprecated MAINTAINER with LABEL

* chore(dockerfile): use gid/uid 10111 for the spinnaker user

* chore(dockerfile): make docker builds more cacheable

Dockerfile.compile

@@ -3,7 +3,7 @@ RUN apk add --update \
     openjdk11 \
     openjdk8 \
     && rm -rf /var/cache/apk
-MAINTAINER sig-platform@spinnaker.io
+LABEL maintainer="sig-platform@spinnaker.io"
 ENV JAVA_HOME /usr/lib/jvm/java-11-openjdk
 ENV JDK_18 /usr/lib/jvm/java-1.8-openjdk
 ENV GRADLE_USER_HOME /workspace/.gradle

Dockerfile.slim

@@ -1,8 +1,9 @@
 FROM alpine:3.11
-MAINTAINER sig-platform@spinnaker.io
-COPY gate-web/build/install/gate /opt/gate
+LABEL maintainer="sig-platform@spinnaker.io"
 RUN apk --no-cache add --update bash openjdk11-jre
-RUN adduser -D -S spinnaker
+RUN addgroup -S -g 10111 spinnaker
+RUN adduser -S -G spinnaker -u 10111 spinnaker
+COPY gate-web/build/install/gate /opt/gate
 RUN mkdir -p /opt/gate/plugins && chown -R spinnaker:nogroup /opt/gate/plugins
 USER spinnaker
 CMD ["/opt/gate/bin/gate"]

Dockerfile.ubuntu

@@ -1,8 +1,8 @@
 FROM ubuntu:bionic
-MAINTAINER sig-platform@spinnaker.io
-COPY gate-web/build/install/gate /opt/gate
+LABEL maintainer="sig-platform@spinnaker.io"
 RUN apt-get update && apt-get -y install openjdk-11-jre-headless wget
-RUN adduser --disabled-login --system spinnaker
+RUN adduser --system --uid 10111 --group spinnaker
+COPY gate-web/build/install/gate /opt/gate
 RUN mkdir -p /opt/gate/plugins && chown -R spinnaker:nogroup /opt/gate/plugins
 USER spinnaker
 CMD ["/opt/gate/bin/gate"]