RFR(S): 8213448: [TESTBUG] enhance jfr/jvm/TestDumpOnCrash

[mikhailo.seledtsov at oracle.com]

Please review this change that added these enhancements to the test:
   - added 2 more crash scenarios: crasher via System.halt() and via 
sending a signal
   - removed dumponexit=true from the test, since emergency recording 
should be generated regardless
   - removed -Xint from test cases, thus testing the default configuration
   - simplified the logic of identifying the name of the recording file
   - added diagnostic info to the test


JBS: https://bugs.openjdk.java.net/browse/JDK-8213448
Webrev: http://cr.openjdk.java.net/~mseledtsov/8213448.00/
Testing:
     1. Locally: exercised the test locally on Linux-x64: PASS
     2. Test System: ran 20 times on multiple platforms - All PASS

Thank you,
Misha