RFR:8153584:New jtreg test to verify PathSearchingVirutalMachine.bootClassPath() behaviour

[Alexander Kulyakhtin]

Hi,

Could you, please, review, the following test-only changes (adding a new test).

CR: https://bugs.openjdk.java.net/browse/JDK-8153584 "New jtreg test to verify PathSearchingVirutalMachine.bootClassPath() behaviour" 
Webrev: http://cr.openjdk.java.net/~akulyakh/8153584/

The new test verifies that in the JDK9  PathSearchingVirutalMachine.bootClassPath() always returns an empty string list, regardless of the, now obsolete, sun.boot.class.path property.
In the JDK 8 bootClassPath() used to be verified by a closed test (therefore the CR is closed). We are changing the test and moving it to the open as it verifies the open, public API.

Best regards,
Alexander