test: add known_issues test for #6287

Deleting property in the vm context has no effect
as reported in #6287
The test is moved to the known_issues and will be fixed
with the 5.5 V8 API changes.

test/known_issues/test-vm-deleting-property.js

@@ -0,0 +1,15 @@
+'use strict';
+// Refs: https://github.com/nodejs/node/issues/6287
+
+require('../common');
+const assert = require('assert');
+const vm = require('vm');
+
+const context = vm.createContext();
+const res = vm.runInContext(`
+  this.x = 'prop';
+  delete this.x;
+  Object.getOwnPropertyDescriptor(this, 'x');
+`, context);
+
+assert.strictEqual(res.value, undefined);