RFR: 8236075: Minor bootstrap improvements

[Claes Redestad]

Hi,

some minor cleanups and enhancements in and around java.lang.ClassLoader
which add up to a small startup improvement:

- Remove use of Vector/Hashtable from ClassLoader, along with a few
   other improvements/modernizations.
- Refactor ClassLoader::sys_paths/user_paths so that they're initialized
lazily but also published safely

Webrev: http://cr.openjdk.java.net/~redestad/8236075/open.01/
Bug:    https://bugs.openjdk.java.net/browse/JDK-8236075

Testing: tier1-3

Thanks!

/Claes