[Nestmates] RFR: 8199309: [Nestmates] The new Class nestmate methods should have SecurityManager checks

[David Holmes]

webrev:  http://cr.openjdk.java.net/~dholmes/8199309/webrev/
bug: https://bugs.openjdk.java.net/browse/JDK-8199309

Mandy noted that getNestHost/getNestMembers should have security manager 
checks consistent with the existing getEnclosingClass et al, and this 
was confirmed in discussion with the EG.

isNestMateOf does not need a security check as it never exposes a Class 
instance. It is reworked to avoid the security check put inside getNestHost.

The existing test is updated to run a second time with the default 
security manager and policy in use (for which we need to add an empty 
policy file for jtreg to "use".)

A new test is added to trigger the expected SecurityExceptions.

Thanks,
David