RFR: 8301169: java/net/httpclient/ThrowingSubscribersAsInputStream.java, ThrowingSubscribersAsInputStreamAsync.java, and other httpclient tests failing on windows: Unable to establish loopback connection

[Daniel Fuchs]

The HttpClient Throwing* tests are creating a lot of HttpClient instances and have been observed failing on Windows from time to time with the error:  Unable to establish loopback connection.

To try and mitigate the issue here is a change that will wait for the previous client to be GC'ed before creating the new one. Hopefully that should reduce the cases where these tests fail due to resource exhaustion.

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Commit messages:
 - 8301169

Changes: https://git.openjdk.org/jdk/pull/13644/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13644&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301169
  Stats: 66 lines in 3 files changed: 66 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13644.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13644/head:pull/13644

PR: https://git.openjdk.org/jdk/pull/13644