This is a known issue with the 7.2.1 OVA and VMX image. The fix is to run these commands immediately following completion of ./amp-install in the ova. This will be fixed in the 7.2.3 ova/vmx.
cat /etc/httpd/conf/ssl.crt/server.crt /etc/httpd/conf/ssl.key/server.key > /etc/httpd/conf/ssl.pem
chmod 0600 /etc/httpd/conf/ssl.pem
chown root.root /etc/httpd/conf/ssl.pem
service lighttpd restart > /dev/null
The root cause is a missing ssl.pem file that prevents lighttpd from starting up which prevents the web gui from coming online.