java: add graphviz to container image

[averikitsch]

For sample GoogleCloudPlatform/java-docs-samples#1610
Reference node PR #31

[averikitsch]

@grayside any reason you used ; instead of &&?

[grayside]

Not sure how I missed this notification, sorry. Since I was asked I'll go ahead and fill in my answer.

The change in this PR ended up on:

RUN apt-get update -y && \
    apt-get install -y graphviz && \
    rm -rf /var/lib/apt/lists/*

However, I generally recommend (and use) something more like this (from the node-12 image)

RUN set -ex; \
  apt-get update -y; \
  apt-get install -y \
    graphviz \
    ; \
  rm -rf /var/lib/apt/lists/*

Reasons I do this:

• Semicolons are less visually intrusive
• set -e preserves the "stop-on-error" behavior of &&
• set -x outputs the executed commands during build, removing some of the mystery when reading build logs
• One package per line makes diffs easier to read, especially once you get more than ~5 packages.