Use mock to build rpm packages and preparing initramfs

1) (docker) sudo command was removed from docker.
User is now placed in docker group and can
work access docker socket without sudo
2) (rpm) rpm packages now build using mock without sudo
3) (bootstrap) initramfs is now prepared in mock env

Notes:
- Ask user to relogin, in order to correctly process group membership
- Fix issue with multistrap version
- Improve nodejs support and installation
- Old files saved for checking and should be removed in future

Change-Id: I7828b6e80b9b60c977aa4ab3c39eaa71cbad7982