Concretize preserves deptypes (#2681)

lib/spack/spack/__init__.py

lib/spack/spack/cmd/graph.py

lib/spack/spack/graph.py

lib/spack/spack/spec.py

lib/spack/spack/test/cmd/install.py

lib/spack/spack/test/optional_deps.py

lib/spack/spack/test/spec_dag.py

.../repos/builtin.mock/packages/dt-diamond-bottom/package.py

...ck/repos/builtin.mock/packages/dt-diamond-left/package.py

...k/repos/builtin.mock/packages/dt-diamond-right/package.py

var/spack/repos/builtin.mock/packages/dt-diamond/package.py