RFR: 8292044: HttpClient doesn't handle 102 or 103 properly [v2]

[Jaikiran Pai]

> Can I please get a review of this change which proposes to fix https://bugs.openjdk.org/browse/JDK-8292044?
> 
> The linked JBS issue notes two parts to fixing this. Part one is to (internally) ignore the intermediate 1xx informational responses, in the client and wait for subsequent final response from the server. Part two is to introduce newer APIs to let applications using HttpClient, to have access to these intermediate response (codes). This commit (only) addresses part one. Part two is out of scope of this change and a separate issue will be opened to address it (at a later time).
> 
> The commit in this PR introduces a check to see if the returned response is an informational response (as defined by RFC-2616 https://www.rfc-editor.org/rfc/rfc2616#page-58). If the response code is between 102 and 199 (inclusive), then this change ignores that response and keeps waiting for a subsequent final response from the server.
> 
> The request timeout (if set) will _not_ be reset when a intermediate informational response is received (and we ignore it). The request timeout handling continues to be the same as what it is currently and will span from the request start till the final response is received. If no final response is received within the duration of request timeout (if set) then the application will continue to receive a request timeout exception.
> 
> A new test class has been introduced to reproduce the issue and test the fix. The test tests both HTTP/1.1 and HTTP2. 
> 
> tier1, tier2 and tier3 testing is in progress.

Jaikiran Pai has updated the pull request incrementally with two additional commits since the last revision:

 - add a test to verify request timeout when server only sends 1xx responses
 - review comment - Additional log a Log.logTrace message for ignored informational response

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10169/files
  - new: https://git.openjdk.org/jdk/pull/10169/files/696a6bfc..cfc4b666

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10169&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10169&range=00-01

  Stats: 50 lines in 2 files changed: 48 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10169.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10169/head:pull/10169

PR: https://git.openjdk.org/jdk/pull/10169