Under some environmental conditions JShell tests hang.

It is not related to the specific test, but related to the launching of JShell.

This bug will serve as the repository of those failures and are the parent issue of those already filed against specific tests.

Please note: This only for tests which fail with --

test result: Error. Agent error: java.lang.Exception: Agent timed out with a timeout of 120 seconds; check console log for any additional details

A fix for this is, hopefully, in the works (waiting on CCC review): JDK-8169519

Note also: this issue should not be confused with JDK-8163250 which is only for tests which fail with "Error while cleaning up threads after test"