RFR: 8270290: NTLM authentication fails if HEAD request is used

[Alex Kasko]

When HEAD request is used with a proxy (or a server) that requires NTLM, authentication fails when server returns large (8kb+) body along with NTLMSSP_CHALLENGE response.

Proposed fix is to check for ongoing NTLM auth in `reset()` and consume the response body in this case.

Alternatively the whole check for `HEAD` method in `reset()` can be dropped.

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Commit messages:
 - 8270290: NTLM authentication fails if HEAD request is used

Changes: https://git.openjdk.java.net/jdk/pull/4753/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4753&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270290
  Stats: 264 lines in 2 files changed: 263 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4753.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4753/head:pull/4753

PR: https://git.openjdk.java.net/jdk/pull/4753