Investigate BoomerAMG quality for linear elasticity in parallel

Investigate a possible bug in computing AMG's hierarchy for linear elasticity problems in parallel To reproduce via MFEM: `mpirun -np 4 ./ex2p -m ../data/beam-tet.mesh -elast -vdim` cc @pazner @tzanio See details in https://github.com/mfem/mfem/pull/4412