teach httpclient adapter how to raise faraday exceptions

[technoweenie]

  2) httpclient using HTTPS proxy with HTTPS server fails to connect
     Failure/Error: expect { conn.get 'foo' }.to raise_error(Faraday::ConnectionFailed)

       expected Faraday::ConnectionFailed, got #<HTTPClient::KeepAliveDisconnected: HTTPClient::KeepAliveDisconnected: > with backtrace:
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/session.rb:808:in `block in parse_header'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/session.rb:801:in `parse_header'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/session.rb:653:in `connect_ssl_proxy'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/ssl_socket.rb:24:in `create_socket'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/session.rb:752:in `block in connect'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/session.rb:748:in `connect'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/session.rb:511:in `query'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient/session.rb:177:in `query'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient.rb:1242:in `do_get_block'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient.rb:1019:in `block in do_request'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient.rb:1138:in `rescue in protect_keep_alive_disconnected'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient.rb:1131:in `protect_keep_alive_disconnected'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient.rb:1014:in `do_request'
         # /usr/local/bundle/gems/httpclient-2.8.3/lib/httpclient.rb:856:in `request'
         # /usr/local/bundle/bundler/gems/faraday-be097190e962/lib/faraday/adapter/httpclient.rb:42:in `call'
         # /usr/local/bundle/bundler/gems/faraday-be097190e962/lib/faraday/rack_builder.rb:153:in `build_response'
         # /usr/local/bundle/bundler/gems/faraday-be097190e962/lib/faraday/connection.rb:504:in `run_request'
         # /usr/local/bundle/bundler/gems/faraday-be097190e962/lib/faraday/connection.rb:207:in `get'
         # ./spec/secure_spec.rb:30:in `block (4 levels) in <top (required)>'
         # ./spec/secure_spec.rb:30:in `block (3 levels) in <top (required)>'
     # ./spec/secure_spec.rb:30:in `block (3 levels) in <top (required)>'