ART: Create and use multiple core images

Update test infrastructure to understand several core variants.
Now compiles three core.art/oat variants:

* core.art/oat, default-compiled
* core-interpreter.art/oat, interpret-only
* core-optimizing.art/oat, optimizing compiler

The run-test variant implies which core variant is used.

Change-Id: Ieeaf2df90faee2b04c209b950897e77806205fe4