RFR(S): 8223396: [TESTBUG] several jfr tests do not clean up files created in /tmp

[mikhailo.seledtsov at oracle.com]

Please review this change that converts all uses of 
Files.createTempFile/createTempDirecotry in JFR tests to
use corresponding test library Utils methods. Using test.lib.Utils for 
this purpose is a recommended practice
for JDK tests.

I have also create a new method in jdk.test.lib.Utils: createTempDirectory()

     JBS: https://bugs.openjdk.java.net/browse/JDK-8223396
     Webrev: http://cr.openjdk.java.net/~mseledtsov/8223396.00/
     Testing:
         1. Locally: ran the affected tests (Mac) - All PASS
         2. test cluster: running jdk_jfr and tier1 - in Progress

Note: to be safe, I will not integrate this until Monday morning.


Thank you,
Misha