RFR: 8273401: Disable JarIndex support in URLClassPath [v2]

[wxiang]

> There is a bug for URLClassPath.findResources with JarIndex.
> Currently, there was agreement on dropping the support from the URLClassLoader implementation but it was suggested that it should be disabled for a release or two before the code is removed. 
> A system property can be used to re-enable JarIndex support in URLClassPath.
> 
> The PR includes:
> Disable JarIndex support in URLClassPath by default.
> Add system property jdk.net.URLClassPath.enableJarIndex to re-enable JarIndex support.

wxiang has updated the pull request incrementally with one additional commit since the last revision:

  add isEmpty check

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5524/files
  - new: https://git.openjdk.java.net/jdk/pull/5524/files/6a6e7b15..8dd17484

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5524&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5524&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5524.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5524/head:pull/5524

PR: https://git.openjdk.java.net/jdk/pull/5524