otherwise yum-config-manager is not found sometimes.

  In case download from shacache fails, the upgrade should safely stop and be able to run again

  Include Debian 7 and 8
  Include ansible playbook to automate the build
  Include Ubuntu 15.04 and Ubuntu 14.04
  Include configuration for CentOS 6.7 and 7.2

  - Use crontab instead rc.local for start up
  - Include log on the run
  - Make script retry in case of failure (ie.: Network is not ready yet)
  - Pass PATH variable for slapos format, on cron it cannot find few binaries

 - ensure that gpg key for opensuse repo is present
 - pre-fill cache with specific node to faster bootstrap in re6stnet-upgrader
 - re6stnet-upgrader doesn't fail if previous version of package was also a re6st-node
 - repositories keys have to be installed before updating package cache
 - re6stnet-upgrader ensures that service is enabled
 - only update once package cache in re6stnet-upgrader