adds `yaml_utf8` option to master config

Reference about this config value: http://docs.saltstack.com/en/latest/ref/configuration/master.html#yaml-utf8
Reference why this might be useful: https://github.com/saltstack/salt/issues/3436#issuecomment-61225863
Merge pull request #63 from sinnerschrader/feature/add_yaml_utf8_to_master_config

adds `yaml_utf8` option to master config