Use Oracle JDK

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It's possible licensing issues will require us to return to the openjdk, but we are anticipating TIER will have the appropriate permissions. We must certainly do testing with the Oracle JDK no matter what, so let's get that documented as well.

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Should also set JAVA_HOME

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https://github.com/Unicon/shibboleth-idp-dockerized/wiki/Switching-to-the-Oracle-JVM#using-your-custom-image