RFR 8016325: JVM hangs verifying system dictionary

[Coleen Phillimore]

Summary: Minimize redundant verifications of Klasses.

Also removed is_metadata() because checking that metadata is not in the 
Java heap doesn't make sense anymore and could slow down verification 
also.   Some cases that aren't statically checked by the compiler now 
call is_metaspace_object() under assert for verification.

Tested by nsk.quick.testlist, and failing SQE test.

open webrev at http://cr.openjdk.java.net/~coleenp/8016325/
bug link at http://bugs.sun.com/view_bug.do?bug_id=8016325
local bug link https://jbs.oracle.com/bugs/browse/JDK-8016325

thanks,
Coleen