* lib/webrick/https.rb: check ssl context of virtual host.
* lib/webrick/ssl.rb: ensure to return ssl context.
* test/webrick/test_https.rb: test returned cert is correct.
  [Feature #13729][ruby-dev:50173]

Author: Tietew <tietew@gmail.com>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59351 b2dd03c8-39d4-4d8f-98ff-823fe69b080e