Edit VM image and make passwordless

Either with guestfish or virt-edit this can be done

virt-edit -d centos /etc/passwd -e ‘s/^root:.*?:/root::/’

virsh # start centos
Domain centos started

virsh # console centos
Connected to domain centos
Escape character is ^]

CentOS Linux 7 (Core)
Kernel 3.10.0-229.el7.x86_64 on an x86_64

localhost login: root
Last failed login: Thu Sep 10 09:41:52 UTC 2015 on ttyS0
[root@localhost ~]#