RFR 8223065: Add jcmd to get the listen address of the debugger

[Schmelter, Ralf]

Thanks for the review.

I've update the webrev to use explicit NULL checks: https://bugs.openjdk.java.net/browse/JDK-8223065

And I now use the pointer to the first byte in the result to split the property value, since I might need the calculate the pointer past the last character (if the prop ends with ':').

I cannot see the SEGV, but I've scheduled the patch to be tested in our nightly build again, so maybe I can reproduce it there.

Best regards,
Ralf