spec/ruby/library/etc/getlogin_spec.rb: Use `logname` as an expected result
spec/ruby/library/etc/getlogin_spec.rb: Use `logname` as an expected result

It had used `id -un`, but it is not always equal to `Etc.getlogin`.
`id` returns the current user of the process, and `Etc.getlogin` returns
the user name logged in on the controlling terminal of the process.

This change uses `logname` by default.  `id` remains as a fallback since
there seem to be some platforms where `logname` is not available:
https://github.com/ruby/spec/commit/49576b417ca3704cfb8271d2545c06c076c10cbc

git-svn-id: ab86ecd26fe50a6a239cacb71380e346f71cee7d@61759 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

eregon/rubyspec,nobu/rubyspec,ruby/spec,ruby/rubyspec,eregon/rubyspec,ruby/rubyspec,eregon/rubyspec,ruby/spec,nobu/rubyspec,ruby/spec,nobu/rubyspec