Add negotiated SSL protocol and cipher to Net::HTTP debug output

[bdewater]

This makes is easier to verify what Ruby has negotiated with the server. An example of why you'd want to double check; for credit card payment data the PCI DSS mandates that TLS 1.1 or newer is used after June 30.

Example output:

opening connection to stripe.com:443...
opened
starting SSL for stripe.com:443...
SSL established, protocol: TLSv1.2, cipher: ECDHE-RSA-AES128-GCM-SHA256

[bdewater]

I've taken a slightly different approach to fix this in activemerchant/active_merchant#2862 to fix my immediate problem. This made me wonder if we should expose this in a way more similar to peer_cert or just keep it as is. Thoughts?

ruby/lib/net/http.rb

Lines 888 to 893 in 96db72c

	def peer_cert
	if not use_ssl? or not @socket
	return nil
	end
	@socket.io.peer_cert
	end

[bdewater]

Come to think of it - if this is something you care about Ruby 2.5 already offers min_version= and max_version=, and the connection will fail if those cannot be met. I think this logging change is fine for diagnostics and we don't need reader methods.

[bdewater]

@yuki24 is there anything I can do to get this merged?

[bdewater]

https://bugs.ruby-lang.org/issues/15009 has been merged, thank you!