Merge pull request #304 from spotify/rugvip/cli-helpers

cli: add helpers for running child processes and error handling in commands

scripts/cli-e2e-test.js

@@ -62,6 +62,9 @@ function print(msg) {
 }
 
 async function waitForExit(child) {
+  if (child.exitCode !== null) {
+    throw new Error(`Child already exited with code ${child.exitCode}`);
+  }
   await new Promise((resolve, reject) =>
     child.once('exit', code => {
       if (code) {