Add bootstrap script for OpenVZ containers

This script can be run when a new OpenVZ container has been created and
started, to automatically prepare it for Ansible management. It will
install Python support and set up users SSH key for easy remote access
via SSH.
Remove 'ansible_managed' from OpenVZ templates
Make vzbackup script more robust

vzbackup script will now automatically put new container backups in
/var/lib/vz/dump if a backup path is not specified on the command line.
Clean up OpenVZ role and add configuration script

- tasks in 'openvz' role have been rewritten to use YAML syntax instead
  of inline syntax;

- new default container configuration file has been added, which
  automatically calculates memory and disk settings for new containers
  based on number of planned containers and available resources;
Update CHANGELOG.md
Merge pull request #139 from drybjed/role/openvz

Updates in 'openvz' role