RFR: 8286293: Tests ShortResponseBody and ShortResponseBodyWithRetry should use less resources

[Daniel Fuchs]

Hi,

Please find here a simple test fix that re-architecture ShortResponseBody for better resource usage.
The test is split to test GET and POST separately and avoids testing GET twice.

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Commit messages:
 - 8286293: Tests ShortResponseBody and ShortResponseBodyWithRetry should use less resources

Changes: https://git.openjdk.java.net/jdk/pull/8569/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8569&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286293
  Stats: 501 lines in 5 files changed: 315 ins; 172 del; 14 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8569.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8569/head:pull/8569

PR: https://git.openjdk.java.net/jdk/pull/8569