[Enh]: 8230091: Add verification of clean_catch_blocks

[Nils Eliasson]

Hi,

This patch adds some verfication of clean_catch_blocks in zBarrierSetC2. 
This would have catched the bug i recently fixed: JDK-8229970

Bug: https://bugs.openjdk.java.net/browse/JDK-8230091

Webrev: http://cr.openjdk.java.net/~neliasso/8230091/webrev.01/

Regards,

Nils