refactor User#groups to not use `id`

[johrstrom]

Using id to parse ids may be problematic due to some groups having spaces in the name. Specifically domain users in some AD systems.

ood_support/lib/ood_support/user.rb

Line 90 in 7e24084

`id -G #{name}`.split(' ').map {|g| Group.new(g.to_i)}

See OSC/nginx_stage#45

Maybe it should look more like CurrentUser in ondemand.
https://github.com/OSC/ondemand/blob/dda7c0dd579765c5f983874f6f139f083804f883/apps/dashboard/app/models/current_user.rb#L42-L50

I'm not sure how to replicate as I can't create a unix group with a space in it.