shell: Rewrite 'block_get_desc' to avoid HTML parsing

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Link from physical volumes to their volume group or mdraid.

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Link from volume groups and mdraids to their physical volumes.

Closes #1073
Reviewed-by: Stef Walter <stefw@redhat.com>