RFR: 8274779: HttpClient and HttpsClient incorrectly check request method when set to POST

[Evan Whelan]

Hi,

Please review my fix for JDK-8274779 which changes how HttpClient and HttpsClient  checks for equality when comparing request methods. 

When `HttpURLConnection.setRequestMethod` is passed `new String("POST")` rather than the "POST" String literal, the old behaviour resulted in broken HttpClients being reused from the `KeepAliveCache`. 

This is because a call to `HttpClient.available()` was never reachable due to identity equality being used instead of logical equality.

The test case uses an injected KeepAliveCache, to which we put a HttpClient that is unavailable. By comparing the initial HttpClient's `connectTimeout` value to the "cached" client's connectTimeout (1234 vs 4321 respectively) we can assert that these values should never be equal as a new HttpClient should be created in cases where we can no longer use the cached one.

All CI testing is green for this fix.

Kind regards,
Evan

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Commit messages:
 - 8274779: HttpClient and HttpsClient incorrectly check request method when set to POST

Changes: https://git.openjdk.java.net/jdk/pull/5964/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5964&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274779
  Stats: 143 lines in 3 files changed: 141 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5964.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5964/head:pull/5964

PR: https://git.openjdk.java.net/jdk/pull/5964