RFR: Filter out not compilable methods to avoid false assertion

[Zhengyu Gu]

Compiler actually encounters some methods that are not compilable, such 
as methods having breakpoints set or being redefined, they should be 
filtered out, cause they are not really gotten compiled.

Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/filter_bad_method/webrev.00/

Test:

   tier2_gc_shenandoah and vmBasetest/nsk where failures were seen.


Thanks,

-Zhengyu