RFR (M): 8231595 [TEST] develop a test case for SuspendThreadList including current thread

[serguei . spitsyn]

Please, review fix for test enhancement:
  https://bugs.openjdk.java.net/browse/JDK-8231595
Webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2019/8231595-jvmti-susp-tlist.1/

Summary:
  New test is a coverage for the JVMTI bug:
    https://bugs.openjdk.java.net/browse/JDK-8217762
      SuspendThreadList won't work correctly if the current thread is 
not last in the list

  It provides a prove the bug JDK-8217762 does not exist
  as the test is passed with the current implementation.

Thanks,
Serguei