[jdk11u] RFR: 8276774: Cookie stored in CookieHandler not sent if user headers contain cookie

[Martin Doerr]

Almost clean Backport of JDK-8276774. One hunk in Stream.java required manual integration because the switch expression doesn't exist in 11u. The test needed adaptations because SimpleSSLContext is located at a different place in 11u and `Stream.toList()` is unavailable (see 2nd commit).

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Commit messages:
 - Adapt new test to JDK11.
 - Backport 03debf277537135974d3f55e3a5c7cf6842ee5e0

Changes: https://git.openjdk.java.net/jdk11u/pull/18/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u&pr=18&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276774
  Stats: 82 lines in 4 files changed: 35 ins; 18 del; 29 mod
  Patch: https://git.openjdk.java.net/jdk11u/pull/18.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u pull/18/head:pull/18

PR: https://git.openjdk.java.net/jdk11u/pull/18