Various fixes for 0.9-build-deps.
- Install libtirpc-devel so that libmesh includes XDR I/O.
- Configure libmesh with MPI.
- Change flags for SAMRAI to avoid snazzy new-architecture instructions (so github runners don't crash).
- Reorder the sccache and cmake downloads since a rebuild is already required.
- Add
/root/.bashenv
and a docker environment variable so that scripts can load and use the MPI module.