playbook: don't change default DNS server during vm-bootstrap
The VM will use the DNS server coming from qemu-kvm (see https://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29) so it will actually use the DNS from the host machine.
The VM will use the DNS server coming from qemu-kvm (see https://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29) so it will actually use the DNS from the host machine.