Add more steps to the Troubleshooting guide for network issues and connectivity problems

From: https://github.com/3scale/documentation_site/issues/397

We are receiving more and more tickets around failed SSL connections. Quite often with a 408 timed out response.

openssl s_client module is a useful way to check if the client can connect via SSL to the host, it should give some clear view as to what might be failing on the client side. We need to add other steps though.

tcp dump
check access logs

Please add more cc @3scale/support