RFR: 8213269: convert test/hotspot/jtreg/runtime/memory/RunUnitTestsConcurrently to gtest

[Mikhailo Seledtsov]

This is a preliminary review. I would like to get the initial feedback before I proceed with conversion of the remaining tests.

Here is what I did so far:
  - created a UnitTestThread and a main test runner, based on gtests with similar needs
  - moved the original code from HotSpot internals (so called hotspot internal tests: src/hotspot/share/memory/virtualspace.cpp)
    to the newly created gtest while wrapping it into a TestReservedSpace class. I did not change the code of the test.
  - removed invocations from whitebox.cpp

Testing:
  - ran GTestWrapper on usual platforms - All PASS
  - ensured that ReservedSpaceConcurrent is in the logs and passed

After gathering the feedback my plan is:
Plan:
  - move the remaining internal Memory/VirtualSpace tests into a gTest
    - I am thinking about using separate files for each test
  - create a common file for UnitTestThread and MultiThreadTestRunner to reuse the code

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Commit messages:
 - Removing RunUnitTestsConcurrently.java from TEST groups
 - Using original duration and concurrency factor
 - Removing test reference from whitebox and the original jtreg test
 - Cleanup
 - Fixed build issue, minor cleanup
 - Moved reserve_memory_special for Windows to GTest
 - Removed empty test from AIX and BSD
 - Linux variant of reserve_memory_special_concurrent to GTest
 - Factored concurrent test runner helpers into its own file, for inclusion from multiple files
 - Converted TestVirtualSpace_test to gtest
 - ... and 9 more: https://git.openjdk.java.net/jdk/compare/2be60e37...4076519f

Changes: https://git.openjdk.java.net/jdk/pull/2436/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2436&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8213269
  Stats: 1301 lines in 13 files changed: 632 ins; 664 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2436.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2436/head:pull/2436

PR: https://git.openjdk.java.net/jdk/pull/2436