[jdk11u-dev] RFR: 8278067: Make HttpURLConnection default keep alive timeout configurable

[Goetz Lindenmaier]

I backport this for parity with 11.0.17-oracle. 

I had to resolve KeepAliveCache because the indentation differs.

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Commit messages:
 - Backport d8f44aa39e921594505864e6270f42b745265293

Changes: https://git.openjdk.org/jdk11u-dev/pull/1193/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1193&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8278067
  Stats: 256 lines in 4 files changed: 242 ins; 1 del; 13 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1193.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1193/head:pull/1193

PR: https://git.openjdk.org/jdk11u-dev/pull/1193