RFR: JDK-8075706 : Policy implementation does not allow policy.provider to be on the class path

[Sean Mullan]

Please review this change to use the system class loader to locate a 
policy provider specified with the policy.provider security property. 
The current implementation tries to load the provider using the 
extension class loader. This will no longer work when the extension 
mechanism is removed, which is proposed as part of JEP 220: 
http://openjdk.java.net/jeps/220

webrev: http://cr.openjdk.java.net/~mullan/webrevs/8075706/webrev.01/
Thanks,
Sean