fix(xen-api/cli): dont run default export when imported by ESM

Fix a bug in `@xen-orchestra/xapi` introduced by c3e0308ad

`module.parent` is `null` when the module is the entry point but `undefined` when imported via ESM.

packages/xen-api/src/cli.js

@@ -130,6 +130,6 @@ async function main(createClient) {
 }
 export default main
 
-if (!module.parent) {
+if (module.parent === null) {
   main(require('./').createClient).catch(console.error.bind(console, 'FATAL'))
 }