test: allow Chrome sandbox opt-out (--no-sandbox)

In some environments, e.g. containers or in some cases macOS,
headless Chrome may not work with the sandbox enabled. This exposes
an escape hatch to run tests in those environments.

Example use:

```sh
yarn bazel test \
  //packages/angular_devkit/build_angular:build_angular_karma_test \
  --test_env=PUPPETEER_EXECUTABLE_PATH="/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" \
  --test_env=CHROME_NO_SANDBOX=1
```

modules/testing/builder/projects/hello-world-app/karma.conf.js

@@ -45,7 +45,10 @@ module.exports = function(config) {
     customLaunchers: {
       ChromeHeadlessCI: {
         base: 'ChromeHeadless',
-        flags: ['--disable-gpu'],
+        flags: [
+          '--disable-gpu',
+          ...(process.env.CHROME_NO_SANDBOX === '1' ? ['--no-sandbox'] : []),
+        ],
       },
     },
     singleRun: false,

packages/angular_devkit/build_angular/test/hello-world-lib/projects/lib/karma.conf.js

@@ -40,7 +40,10 @@ module.exports = function (config) {
     customLaunchers: {
       ChromeHeadlessCI: {
         base: 'ChromeHeadless',
-        flags: ['--disable-gpu']
+        flags: [
+          '--disable-gpu',
+          ...(process.env.CHROME_NO_SANDBOX === '1' ? ['--no-sandbox'] : []),
+        ],
       }
     },
     singleRun: false