The test code in:
test/hotspot/jtreg/testlibrary/ctw/src/sun/hotspot/tools/ctw/ClassPathJimageEntry.java
uses several APIs in ImageReader which need to be removed for the Valhalla work.

Since the JRT file system offers an equivalent view onto the underlying jimage data, and is more stable/well-defined than the other ImageReader APIs, it seems best to just migrate it to using that instead.

Since the initial refactoring of ImageReader is going into JDK mainline first, this change also needs to go into the mainline.