docker: skip update/upgrade, upstream does it

Just update the base and then rebuild the image to get updates.
docker: combine useradd and sudoers layers

Less layers is better
vagrant: switch centos box to chef/centos-6.5

Fixes #1
vagrant: use centos-6.6 for centos6 vm

Replaces centos65 vm
vagrant: Add centos7 vm based on CentOS 7.0