RFR(S): 8235454: [TESTBUG] Basic test for JFR event streaming for jdk_jfr_sanity

[mikhailo.seledtsov at oracle.com]

Please review this change that introduces a very simple basic/sanity 
test for JFR streaming, and adds this test to jdk_jfr_sanity (which runs 
in tier-1).

     JBS: https://bugs.openjdk.java.net/browse/JDK-8235454
     Webrev: http://cr.openjdk.java.net/~mseledtsov/8235454.00/
     Testing:
         1. Ran this test over 200 times on multiple platforms in the 
test cluster: ALL PASS

          2. Ran the group jdk_jfr_sanity 80 times: ALL PASS

Thank you,
Misha