RFR: 8284331: Add sanity check for signal handler modification warning.

[Kevin Walls]

On Tue, 5 Apr 2022 10:37:26 GMT, Kevin Walls <kevinw at openjdk.org> wrote:

> A sanity check using "jcmd VM.info" to catch the signal handler modification warning: it should never trigger during this test.

(adding a note to trigger email notification, as that appears lost...)

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PR: https://git.openjdk.java.net/jdk/pull/8106