Fix #44: Re-Enabling Asciidoctor-diagram usage

[dduportal]

The Pull Request #39 broke the usage of Asciidoctor-diagram.

This pull request aims to fix it, by introducing the following:

• A sample from asciidoctor-diagram doesn't work on alpine based image #44 has been added to validate usage and provide non-regression in future upgrades
• 3 test cases have been introduced to cover the tools that where missing
• Install OpenJDK8-JRE (not the full JDK: I might miss something but we just want to execute with Java)
• Install Graphviz, required for generating diagrams

[EDIT]
The image is built (and updated) on the DockerHub and can be pulled without building it:

docker pull dduportal/docker-asciidoctor:fix-adoc-diagram

[mojavelinux]

We probably want a slightly more complex example to make sure we put some weight on graphviz to verify it works. Perhaps @pepijnve can advise. @pepijnve do you have a go-to example that you use (perhaps from the test suite) that thoroughly tests the graphviz setup?

I'm pretty sure all we need is a JRE.

[dduportal]

The build on my own TravisCI was broken due to the "files owned by root" when cleaning the test cases: https://travis-ci.org/dduportal/docker-asciidoctor/builds/288124855

Just added a fix on the test harness suite to avoid breaking any kind of CI, by using "docker for everything" pattern.

[dduportal]

Hello @mojavelinux!

I just want to be sure I get the goal:

Should we:

• Merge this pull request saying it is solving asciidoctor-diagram doesn't work on alpine based image #44 and plan to add improved tests in the harness?
• Update this pull request to focus on the JRE only (It solves asciidoctor-diagram doesn't work on alpine based image #44 also), and treat graphviz separately?

[mojavelinux]

I'm fine with moving forward and filing a separate issue for strong tests. I just mentioned it because I'm concerned this is going to keep biting us if we don't test it more thoroughly.

[dduportal]

This Pull Request have been merged.

@mojavelinux, the issue #48 has been opened to keep track of the graphviz test weight.
Thanks for your quick feedback and review!

[mojavelinux]

Thanks @dduportal!