Add more debug info

closed server doesn't have useful info.
So call inspect before close.
And add local debug code in comment.

https://rubyci.org/logs/rubyci.s3.amazonaws.com/unstable11x/ruby-master/log/20191215T092405Z.fail.html.gz
```
  1) Failure:
IMAPTest#test_connection_closed_without_greeting [/export/home/rubyci/chkbuild-tmp/tmp/build/20191215T092405Z/ruby/test/net/imap/test_imap.rb:483]:
[Net::IMAP::Error] exception expected, not #<RuntimeError: {:e=>#<Errno::EINVAL: Invalid argument - connect(2) for [::1]:41748>, :server=>#<TCPServer:(closed)>, :port=>41748, :server_addr=>"::1"}>.
```

0 files changed, 0 insertions, 0 deletions