RFR: Allocation failure injection machinery

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/inject-alloc-failure/webrev.01/

Found many bugs in Degenerated GC with this machinery. But it is separate from the rest of the code,
and is useful to have for general testing: for example, to test if baseline without Degenerated GC
fails the same way. Therefore, this patch splits the machinery out.

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey