feat(@angular/cli): read proxyConfig from angular-cli.json

easy proxy config by reading default from angular-cli.json (angular#6240)

Author: ayvazj

tests/e2e/tests/misc/proxy-config.ts

@@ -32,6 +32,17 @@ export default function() {
 
   return Promise.resolve()
     .then(() => writeFile(proxyConfigFile, JSON.stringify(proxyConfig, null, 2)))
+
+    .then(() => ngServe('--proxy-config', proxyConfigFile))
+    .then(() => request('http://localhost:4200/api/test'))
+    .then(body => {
+      if (!body.match(/TEST_API_RETURN/)) {
+        throw new Error('Response does not match expected value.');
+      }
+    })
+    .then(() => server.close(), (err) => { server.close(); throw err; })
+    .then(() => killAllProcesses(), (err) => { killAllProcesses(); throw err; })
+
     .then(() => updateJsonFile('.angular-cli.json', configJson => {
       const app = configJson.defaults;
       app.serve = {
@@ -49,6 +60,8 @@ export default function() {
     .then(() => killAllProcesses(), (err) => { killAllProcesses(); throw err; })
 
     // A non-existing proxy file should error.
+
+    .then(() => expectToFail(() => ng('serve', '--proxy-config', 'proxy.non-existent.json')))
     .then(() => updateJsonFile('.angular-cli.json', configJson => {
       const app = configJson.defaults;
       app.serve = {