Add "--limit-rate " option to curl. Download-only option not needing sudo in installinstallmacos.py

[porteusconf]

2 really trivial feature requests

• (1.) Add something like a --download-only option (which also implies sudo is not needed)
  If I just want to download installers, and not create a disk-image, sudo is not needed it seems. I just commented out these lines 493-495 and as non-admin/non-sudo user, all downloads proceed ok. Of course then it bombs out when it trys to create an image but that's ok cause I did not want the disk-image, just the download.

#    if os.getuid() != 0:
#        sys.exit('This command requires root (to install packages), so please '
#                 'run again with sudo or as root.')

• (2.) Add limit-rate option passed to curl_cme
  Also, for folks like home-users with slow internet, could we add a --limit-rate option to pass to the curl_cmd which seems to slow downloads to 100k/sec in example below.

    curl_cmd = ['/usr/bin/curl', options, '--limit-rate', ' 100k', '--create-dirs',
                '-o', local_file_path]

The curl command used in installinstallmacos.py seems to be able to resume partial-downloads from where it left off. So, with the limit-rate the download of the 6+gig mojave installer could be spread-out over a few days to save bandwidth for zoom, etc.
Finally, If you want me to fork and do a request let me know, but I really don't know python at all ;-). Or maybe I should submit these feature requests to https://github.com/grahampugh/macadmin-scripts

[gregneagle]

Neither is something I need at present so unlikely to spend any time on either any time soon. Seems like you have ways to do these for yourself for now...