[8u] RFR 8216401: Allow "file:" URLs in Class-Path of local JARs

[Zhengyu Gu]

Please review 8u backport of above CR.
JDK13 patch does not apply cleanly. However, the fix itself applies 
cleanly, just not the test.

8u ClassFileInstaller does not have some APIs that exist in JDK13. 
Therefore, I copied/pasted corresponding code from JDK13's 
ClassFileInstaller into the test (writeClassToDisk and writeToDisk).

Original bug: https://bugs.openjdk.java.net/browse/JDK-8216401
Original Webrev: 
https://mail.openjdk.java.net/pipermail/core-libs-dev/2019-January/057868.html
Original review thread: 
https://mail.openjdk.java.net/pipermail/core-libs-dev/2019-January/057868.html

8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8216401-8u/webrev.00/

Test:
   Run attached test case (before and after fix) on Linux 86_64.

Thanks,

-Zhengyu