[jdk15u-dev] Integrated: 8274779: HttpURLConnection: HttpClient and HttpsClient incorrectly check request method when set to POST

[Yuri Nesterenko]

This useful fix should be ported here, too. Clean. All relevant tests pass.

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Commit messages:
 - Backport 45ce06c9f3e9bee7d4bda313c38f0f0e8786a4db

Changes: https://git.openjdk.java.net/jdk15u-dev/pull/123/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk15u-dev&pr=123&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274779
  Stats: 177 lines in 4 files changed: 175 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk15u-dev/pull/123.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk15u-dev pull/123/head:pull/123

PR: https://git.openjdk.java.net/jdk15u-dev/pull/123