built-in modules: missing 'mpi' modules

[HenrikBengtsson]

Need to update https://github.com/ucsf-wynton/lmodweb to handle multi-folder repositories. Currently it doesn't work;

$ Rscript -e R.rsp::rfile software-repositories.md.rsp --postprocess=FALSE                                                               
module_avail() ...                                                                                                                     
List of 1
 $ info:List of 6
  ..$ name       : chr "built-in"
  ..$ maintainer : chr "{{ site.cluster.nickname }} Systems Administrators"                                                            
  ..$ group      : chr "{{ site.cluster.name }}"                                                                                       
  ..$ url        : chr "{{ '/about/contact.html' | relative_url }}"                                                                    
  ..$ contributed: logi FALSE                                                                                                          
  ..$ module_path: chr [1:2] "/etc/modulefiles" "/usr/share/modulefiles"                                                               
Error in spider(module_path, force = force) :
  length(module_path) == 1L is not TRUE                                                                                                
Calls: <Anonymous> ... lapply -> FUN -> module_avail -> spider -> stopifnot