RFR:8153989:Some SVC tests fail on compact2 due to an unnecessary test library dependency

[Alexander Kulyakhtin]

Hi,

Could you, please, review this small tests-only fix:

CR: https://bugs.openjdk.java.net/browse/JDK-8153992 "Some SVC tests fail on compact2 due to an unnecessary test library dependency"
Webrev: http://cr.openjdk.java.net/~akulyakh/8153992/test/testlibrary/jdk/test/lib/ProcessTools.java.udiff.html

Before the fix the ProcessTools.getProcessId() used the ManagementFactory.getRuntimeMXBean() API.
The API is not available on compact2 and below. Therefore the tests failed.

We are changing the ProcessTools.getProcessId() method to use the JDK 9 Process.getPid(). This eliminates the unnecessary dependency making the tests pass on compact2.

I am not sure how acceptable it is to cast from long to int this change. If it is not acceptable we can change the return type to long. 
This however, will cause massive changes throughout the hotspot tests which presently expect getProcessId() to return int.

Best regards,
Alexander