RFR: JDK-8305414: gtest/NMTGtests.java is failing various sub-tests

[Thomas Stuefe]

[JDK-8304815](https://bugs.openjdk.org/browse/JDK-8304815) added the ability to use NMT for better hs-err reporting: we now ask NMT - if enabled - to make sense of otherwise unknown memory locations.

With C-heap blocks, the error printer now prints out a message if a memory location points into a live or dead malloc block. For details, see JDK-8304815 and the comments in mallocTracker.cpp.

The change came with its own gtest, which promptly started to fail intermittently. That failure was caused by a real issue the test found where we accidentally returned from MallocTracker::print_pointer_information() if we encountered unmapped memory (this makes the error intermittent). The return bypassed the block printing code, which made the test fail.

Patch fixes that, and also fixes some debug output in the test.

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Commit messages:
 - JDK-8305414-gtest-NMTGtests.java-is-failing-various-sub-tests

Changes: https://git.openjdk.org/jdk/pull/13296/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13296&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305414
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13296.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13296/head:pull/13296

PR: https://git.openjdk.org/jdk/pull/13296