RFR: 8254802: ThrowingPushPromisesAsStringCustom.java fails in "try throwing in GET_BODY"

[Daniel Fuchs]

Hi,

Please find below a fix that fixes an issue in Http2TestServerConnection - where the 
connection will be closed by the test server if the test server receives a RESET from the client
after the stream has been closed.

This issue has made the ThrowingPushPromisesAsStringCustom test fail from time to time, but
the debug traces have eventually revealed what was the issue:

DEBUG: [readLoop] [818ms] FramesDecoder Got frame: RESET: length=4, streamid=24, flags=0 Error: Stream cancelled
TestServer: Unexpected frame on: 24
RESET: length=4, streamid=24, flags=0 Error: Stream cancelled
Http server reader thread shutdown
java.io.IOException: Unexpected frame
at Http2TestServerConnection.readLoop(Http2TestServerConnection.java:776)
at Http2TestServerConnection$ConnectionThread.run(Http2TestServerConnection.java:438)
Server connection to /127.0.0.1:39830 stopping. 5 streams

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Commit messages:
 - 8254802: ThrowingPushPromisesAsStringCustom.java fails in "try throwing in GET_BODY"

Changes: https://git.openjdk.java.net/jdk/pull/1567/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1567&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254802
  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1567.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1567/head:pull/1567

PR: https://git.openjdk.java.net/jdk/pull/1567