xsdk@0.5.0 (#13682)

Update:
 hypre@2.18.2
 mfem@4.0.1-xsdk
 superlu-dist@6.1.1
 trilinos@12.18.1
 - dtk-3.1
 petsc@3.12.1
 dealii@9.1.1
 pflotran@xsdk-0.5.0
 alquimia@xsdk-0.5.0
 sundials@5.0.0
 plasma@19.8.1
 magma@2.5.1
 amrex@19.08
 slepc@3.12.0
 omega-h@9.29.0
 strumpack@3.3.0
 pumi@2.2.1
 tasmanian@7.0
 phist@1.8.0

New:
 ginkgo@1.1.0
 py-libensemble@0.5.2
 precice@1.6.1
 butterflypack@1.1.0

Add variants:
 ginkgo
 libensemble
 precice
 butterflypack
 strumpack
 trilinos

tasmanian:  use ~openmp only on OSX
precice: disable on OSX
enable sundials+superlu-dist
sundials+superlu-dist requires OpenMP 4.5+ (so enable only for gcc@6.1+)
enable mfem+sundials
enable sundials+petsc+superlu_dist
remove hypre~internal-superlu
petsc: build with +batch on cray
precice: use ~petsc on cray
libensemble: add as runtime dependency for PYTHONPATH