* spec/rubyspec/command_line/dash_upper_s_spec.rb: enable tests on vboxsf
(VirtualBox shared directory) and change tests to match /success$/ to
ignore warnings. This technique is suggested by @unak.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58776 b2dd03c8-39d4-4d8f-98ff-823fe69b080e