RFR: 8256459: java/net/httpclient/ManyRequests.java and java/net/httpclient/LineBodyHandlerTest.java fail infrequently with java.net.ConnectException: Connection timed out: no further information

[Daniel Fuchs]

Hi, 

Please find here a changeset that fixes the infrequent (but annoying) test failures
caused by unexpected ConnectionException "Connection timed out: no further information"
which have been observed to occur on some platforms.

Tests are updated to allow the test server to handle requests concurrently.
PlainHttpConnection is updated to retry connection once if chan::finishConnect fails
early with ConnectionException and the connection timeout has not expired.

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Commit messages:
 - 8256459: java/net/httpclient/ManyRequests.java and java/net/httpclient/LineBodyHandlerTest.java fail infrequently with java.net.ConnectException: Connection timed out: no further information

Changes: https://git.openjdk.java.net/jdk/pull/1716/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1716&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256459
  Stats: 163 lines in 4 files changed: 121 ins; 8 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1716.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1716/head:pull/1716

PR: https://git.openjdk.java.net/jdk/pull/1716