TrfTestsART: Add meta-diff comparison in CA vs. RecExCommon ART tests

Add a meta-diff AOD comparison step to the 4 CA vs. RecExCommon configuration comparison ART tests:

meta-diff --ordered --mode full --diff-format diff def/myAOD_def.pool.root ca/myAOD_ca.pool.root

Tagging @tadej, @mhodgkin, @christos, @nstyles, @jcatmore for info.