test: Fix flaky test-vm-timeout-rethrow

The intention of test case is to make sure that `timeout` property is honored
and the code in context terminates and throws correct exception. However in
test case, the code inside context would complete before `timeout` for windows
and would sometimes fail. Updated the code so it guarantee to not complete
execution until timeout is triggered.

Fixes: nodejs#11261

test/sequential/test-vm-timeout-rethrow.js

@@ -6,7 +6,7 @@ const spawn = require('child_process').spawn;
 
 if (process.argv[2] === 'child') {
   const code = 'let j = 0;\n' +
-               'for (let i = 0; i < 1000000; i++) j += add(i, i + 1);\n' +
+               'while(true);\n' +
                'j;';
 
   const ctx = vm.createContext({