virt-install : ubuntu 16.04 image will not boot

Hello there,

Im a newbie in virsh and i want to report a problem. I need, for a part of my BScthesis to deploy a vm so i can create a custom image to upload it to openstack later.I follow the basic steps to create a vm with virt-install from CLI(https://docs.openstack.org/image-guide/ubuntu-image.html)

- qemu-img create -f qcow2 /var/lib/libvirt/images/custom_ubuntu.qcow2 20G

- virt-install --virt-type kvm --name imagevm --ram 2048 --vcpus 2 --disk /var/lib/libvirt/images/custom_ubuntu.qcow2,format=qcow2 --network network=default --graphics vnc,listen=0.0.0.0 --noautoconsole --os-type=linux --os-variant=ubuntu16.04 --cdrom=/var/lib/libvirt/boot/xenial64mini.iso

- after this, i did the complete installation of the ubuntu 16.04 ( + OpenSSH Server) without any problem

- but after the detach of the boot disk commands :
   -virsh start imagevm --paused
   -virsh attach-disk --type cdrom --mode readonly imagevm "" hda
   -virsh resume imagevm

- the VNCviewer was stuck in the boot screen (screenshot uploaded)

Extras: I tried many ways and changes to the virt-install command + different isos of 16.04 version but i had the same problem. The only time that it works, was with the trusty 14.04 version.

Thank for your time ,

Anastasios