RFR: 8287593: ShortResponseBody could be made more resilient to rogue connections

[Ryan Ernst]

Since ReplyingServer binds to an open port on the system where tests
run, it is possible some other program probes that port while the test
is running. If the probe request does not have request params, the
request is invalid and a test assertion fails. This commit replaces that
assertion with returning a 400 response.

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Commit messages:
 - 8287593: ShortResponseBody could be made more resilient to rogue connections

Changes: https://git.openjdk.org/jdk/pull/9329/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9329&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8287593
  Stats: 43 lines in 1 file changed: 36 ins; 6 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9329.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9329/head:pull/9329

PR: https://git.openjdk.org/jdk/pull/9329