RFR: Check and ensure that Shenandoah-enabled compilations succeed

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/comp-check/webrev.01/

This adds verification code to compiler pipeline that would fail reliably if method had failed to
compile with Shenandoah. This allows us to track compilation bugs before we are forced to inspect
PrintCompilation log chasing the performance regressions. I had to increase max thresholds to make
tier3_gc_shenandoah succeed.

Testing: tier3_gc_shenandoah {fastdebug|release}, specjbb, specjvm

Thanks,
-Aleksey