Add support for AdoptOpenJDK images

[aguibert]

AdoptOpenJDK (https://adoptopenjdk.net/index.html) is a vendor-neutral hosting platform for many highly-tested and supported JDKs. It is also the only place to get an equivalent of the IBM JDK past Java 8 (using the OpenJ9 VM).

A lot of good combinations could be added by supporting AdoptOpenJDK images including:

• OpenJDK 8 w/ OpenJ9 (effectively IBM JDK 8)
• OpenJDK 11 w/ OpenJ9
• OpenJDK 12 w/ OpenJ9 OR Hotspot

These images are quite stable, and are also hosted as official images on DockerHub: https://hub.docker.com/_/adoptopenjdk

[michaelklishin]

If anyone is interested in having support for these JDKs, please submit a pull request. Note that it is not at all obvious whether update-java-alternatives which this tool uses would work with those binary builds.