[common] Config file that use template

[at15]

Transferred, see dyweb/gommon#2 for updates

Inspired by Ansible, we could use a template language in config file, i.e. https://github.com/flosch/pongo2

• remove use of viper, most of the usage should be in the runner part
• support vars, may use https://github.com/mitchellh/mapstructure like viper did
• may need to parse the yaml twice if things like vars are supported

Related issues

• Embed a script language  #51 embed script language
• Config file xephonhq/xephon-b#6 Xephon-B config file