RFR: Fixup roots after partial GC failed

[Zhengyu Gu]

We need to fixup roots after partial failed (just as 
SH::evacuate_and_update()). full-gc's update_roots() does not do the 
trick, 'cause it crosses safepoints, frames moved.


Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/evac_dpt/webrev.00/index.html

Test:
   hotspot_gc_shenandoah (fastdebug and release)



Thanks,

-Zhengyu