RFR: 8316464: 3 sun/tools tests ignore VM flags

[Leonid Mesnik]

I marked tests 
sun/tools/jcmd/TestProcessHelper.java
sun/tools/jinfo/JInfoTest.java
as headless. They used different specific VM options and are not worth executing with other VM flags. 
And fixed 
sun/tools/jstat/JStatInterval.java
Tested with tier1, local execution of tests, and running sun/tools/jstat/JStatInterval.java with different options.

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Commit messages:
 - 8316464

Changes: https://git.openjdk.org/jdk/pull/16078/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16078&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316464
  Stats: 9 lines in 3 files changed: 3 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/16078.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16078/head:pull/16078

PR: https://git.openjdk.org/jdk/pull/16078