ruby: wrap script to disable gems if not installed

ruby, by default, try to load gems on start. If not
present, it fails. As gems brings many deps, this make ruby
unsuitable for routers limited resources.

ruby can avoid to load gems with the option "--disable-gems".
So, a wrap script in the place of /usr/bin/ruby adds this option
if gems are not found.

Also add vendor/site directories
ruby: rdoc can run without gems (with patch)

rdoc seems to be written to run without gem. However,
some internal code still does not check for gems presence.
With a small patch, rdoc can run without gems.

Ref: https://bugs.ruby-lang.org/issues/10196