RFR: 8273401: Disable JarIndex support in URLClassPath

[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.

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Commit messages:
 - 8273401: Disable JarIndex support in URLClassPath

Changes: https://git.openjdk.java.net/jdk/pull/5524/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5524&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273401
  Stats: 13 lines in 3 files changed: 8 ins; 1 del; 4 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