RFR: 8269886: Inaccurate error message for compressed hprof test

[Lin Zang]

The current implementation of hprof Reader for testing always prompts "Can not decompress the compressed hprof file" when there is error for testing gzipped heap dump. This is inaccurate if the gzipped file was decompressed successfully but the hprof file format is incorrect. So the inaccurate error message could be misleading for issue analysis.

This trivial PR refine the error message by simply print "Can not get stack trace from the compressed hprof file", the underlying exception from GZIPInputStream() or HprofReader() would give accurate error info.

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Commit messages:
 - 8269886: Inaccurate error message for compressed hprof test

Changes: https://git.openjdk.java.net/jdk/pull/4685/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4685&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269886
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4685.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4685/head:pull/4685

PR: https://git.openjdk.java.net/jdk/pull/4685