Please check your network on the guest-mashine with:
nmap -sT -O localhost
Check if the ports your are using in your nginx configuration are open.If not, open them in your firewall and check again.
It was a firewall issue inside this machine "intprog/centos7-ez6". It wasn't listening to the port https. I have followed those steps:
firewall-cmd --add-service=https
firewall-cmd --add-service=https --permanent
firewall-cmd --reload
and it all worked.