fix typo: salt.config.{minion_conf=>minion_config}

************* Module salt.cloud.clouds.lxc
salt/cloud/clouds/lxc.py:70: [E1101(no-member), _minion_opts] Module 'salt.config' has no 'minion_conf' member
Merge pull request #11136 from cvrebert/patch-2

fix typo: salt.config.{minion_conf=>minion_config}