The `jrt-fs.jar` shipped in `java-9-openjdk-headless` package is not compatible
with Java 8, which is apparently necessary for some development tools that
themselves run on Java 8 to be able to use the Java 9 JDK shipped in this
package.

One example of this is Intellij IDEA, which means currently it's unable to use
openSUSE provided Java 9 JDK as a project JDK.

A detailed explanation of the issue can be found on OpenJDK bugtracker [1] and
also a test program and steps to reproduce can be found on Ubuntu bugtracker
for their corresponding package [2].

The steps are:

1. zypper in java-9-openjdk-headless java-1_8_0-openjdk-headless
2. download `ReadJrt.java` from [2]
3. /usr/lib64/jvm/java-1.8.0/bin/javac ReadJrt.java
4. /usr/lib64/jvm/java-1.8.0/bin/java ReadJrt /usr/lib64/jvm/java-9/

[1] https://bugs.openjdk.java.net/browse/JDK-8174808
[2] https://bugs.launchpad.net/ubuntu/+source/openjdk-9/+bug/1727002