fixes #11170 - pass quoted args through foreman-rake

Use the special "$@" to correctly pass quoted arguments through
foreman-rake, through su and to the underlying rake command. Ensures
the JSON in this command is unharmed:

foreman-rake config -- -k trusted_puppetmaster_hosts -v '["foo.bar.com"]'

Also swallows the "--" which gets passed through on some versions of
rake.