Provide a flag to enable etcd auth

[kvaps]

Kamaji project uses muti-tenant etcd so it reuqires to make the setup more secured. I think we can provide the following flag:

security:
  enableAuth: true

which should do:

if etcdctl user get root &>/dev/null; then
  echo "User already exists, nothing to do"
else
  etcdctl user add --no-password=true root &&
  etcdctl role add root &&
  etcdctl user grant-role root root &&
  etcdctl auth enable
fi

And in case of false:

etcdctl auth disable