HypreAMG Setup error with block preconditioner

[tlroy]

For PR #1520 and branch roy/block_preconditioner

To get this error, HypreAMG needs to be used as solvers for the blocks in src/smith/differentiable_numerics/tests/test_porous_heat_sink.cpp (need to comment out direct solver options and uncomment the AMG solver options)

Running the test results in this runtime error:

Verification failed: (!err_flag) is false:
--> Error during setup! Error code: 1
... in function: virtual void mfem::HypreSolver::Setup(const mfem::HypreParVector&, mfem::HypreParVector&) const
... in file: linalg/hypre.cpp:4104

The block preconditioner framework was initially devised on commit c6996da3bb081a7ad9d3688ce1a758a30a5ef3a1 on li/DG_advection_diffusion_reaction. There was no error with Hypre AMG for this. Perhaps this is due to MFEM/Hypre changes?