update default box to ubuntu/xenial64; add puppet
update default box to ubuntu/xenial64; add puppet

since Change-Id: I6617283afd798af37e64913b7865cea3c8a62aba the devstack installer
no longer supports trusty and xenial does not have puppet installed by
default

Related-Bug: 1599531
Change-Id: Ic59a768983430149e3f3a4de65606d649bb17693

openstack-dev/devstack-vagrant,openstack-dev/devstack-vagrant