[8u] RFR 8274779: HttpURLConnection: HttpClient and HttpsClient incorrectly check request method when set to POST

[Zhengyu Gu]

Bug: https://bugs.openjdk.java.net/browse/JDK-8274779
Patch: 
https://github.com/openjdk/jdk/commit/45ce06c9f3e9bee7d4bda313c38f0f0e8786a4db

I would like to backport this patch to openjdk8u for parity with Oracle 
8u331.

The original patch applies cleanly, but new test needs to be modified 
for 8u.

1) Adjust test library path and name
2) Removed modules
3) Use ClassFileInstaller to build injection class into inject.jar and 
append it to bootclasspath

8u webrev: http://cr.openjdk.java.net/~zgu/JDK-8274779-8u/webrev.00/

Test:
   jdk_net (including the new test)


Thanks,

-Zhengyu