Check if using SSL before getting SSL conn info.
Check if using SSL before getting SSL conn info.

Was getting this error in a project when running its acceptance tests
against a mocking service that used a `http` schema.
```
undefined method `ssl_version' for #<TCPSocket:(closed)>
$GEMS/bundler/gems/active_merchant-f3d11caabc66/lib/active_merchant/net_http_ssl_connection.rb:7:in `ssl_connection'
$GEMS/bundler/gems/active_merchant-f3d11caabc66/lib/active_merchant/connection.rb:82:in `block (2 levels) in request'
```

varyonic/active_merchant,lcn-com-dev/active_merchant,atxwebs/active_merchant,HealthWave/active_merchant,buttercloud/active_merchant,QuickPay/active_merchant,planetargon/active_merchant,vampirechicken/active_merchant,activemerchant/active_merchant,pinpayments/active_merchant,miyazawadegica/active_merchant,Simplero/active_merchant,Shopify/active_merchant,customerlobby/active_merchant,curiousepic/active_merchant,vanboom/active_merchant,taf2/active_merchant,appfolio/active_merchant,davidsantoso/active_merchant