JDK-8156497 added support to the jar tool for creating and updating MRMJARs, and also some basic test coverage.
There are various other issues in progress that will make creating MRMJARs more straight forward; jar tool support
for --runtime, and javac support. When these pieces are further along, then tools/jar/modularJar/Basic.java should be
re-examined to see if it can be simplified and the coverage extended.

Also, it was noted during the review of JDK-8156497 that the test hard codes the runtime version number to 9. This
should use Runtime.version().major() + 1 instead.