[jdk11u-dev] RFR: 8229486: Replace wildcard address with loopback or local host in tests - part 21

[Goetz Lindenmaier]

I backport this for parity with 11.0.16-oracle.

TcpKeepAliveTest.java does not apply because
   8220083: Use InetAddress.getLoopbackAddress() in place of 127.0.0.1 f...
is missing 

SetIfModifiedSince.java does not apply because
   8226756: Replace wildcard address with loopback or local host in tests - part 18
is missing. 

I included the respective previous changes to these two files in this patch. Backporting these larger
dependencies will cause recursive backports or require resolving. I want to avoid this additional 
effort. In case backports of these other changes are necessary later, one will just have to 
skip the patches to the corresponding files. As the changes are quite simple, this should
be easy enough to do.

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Commit messages:
 - Backport 77d09f0f14bdaafa2e3528c73ee2287338e2ad49

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/902/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=902&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8229486
  Stats: 242 lines in 11 files changed: 155 ins; 11 del; 76 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/902.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/902/head:pull/902

PR: https://git.openjdk.java.net/jdk11u-dev/pull/902