I recently loaded Xenserver 7.0 on a server for experimentation. I installed a Ubuntu 16.04 VM using the template. Every time I install Xen tools with apt-get install xen-tools or using Webmin I lose network connection to the VM on reboot.
I've found that installing from the Xenserver's guest-tools.iso works. I'll post this solution since I couldn't find anything while searching for love or money.
I ran the following commands:
sudo mount /dev/cdrom /mnt
I think I was running into two problems:
1. The apt-get repositories probably have outdated xen-tools.
2. The various guides I found all said that /dev/cdrom shouldn't work, it should be /dev/xvdd.