The following clean-up and refactor of the class loading code is necessary to support CDS in JDK9

[1] Remove code that has been made obsolete by the module changes (such as supporting code used for meta-index file)
[2] Add new whitebox API to be used by CDS-related tests.
[3] Refactor the parsing of classlist files for future enhancements.
[4] Add new APIs in the class loading code to support Oracle CDS enhancements.