Hello
Does the VM have a login screen ?
We have found that sometimes the wrong network adapter is used when importing the image into glance.
What you should do is after using qemu-img convert you should use
head -20 image.vmdk
this will display the adapter that is used in the image and this is the one you need to use when importing into glance. We also found that changing the adapter AFTER importing does not work....we only managed to get it working by importing with all the correct details prior to import.
Also another issue it may be that I think Centos 7 uses the naming of the network adapters something like ens160 and this causes issues with cloud-init but I am not that experienced with that but i know from past experience that Centos had this issue.
Regards
Ben McGuire