RFR: Prepare tests for upstreaming

[Roman Kennke]

I believe if you re-base it on Aleksey's copyright headers change, some
of your own copyright header changes will disappear (e.g.
TestGCBasherWithShenandoah.java).

Other than that, looks ok. Thank you!

Roman


> 1) Added guards for Shenandoah tests in shared directories
> 2) Removed duplicated Critical Native tests, shared them among
> Shenandoah and Epsilon.
> 
> 
> Webrev:
> http://cr.openjdk.java.net/~zgu/shenandoah/test_reshuffle/webrev.00/
> 
> 
> Test:
>   Eyeball tier1_gc_1 and tier3_gc_shenandoah, make sure tests are ran.
> 
> Thanks,
> 
> -Zhengyu