fix(tests): adapt app.json fixtures and tini test for env processing

Pre-set LOCAL_DOMAIN in the tini test so mastodon's required env var
resolves, and replace unsupported `generator: "echo 5"` with `value: "5"`
in the nodejs-express and dockerfile fixtures so WEB_CONCURRENCY no
longer aborts deploys via the new app.json env processor.

tests/unit/app-json.bats

@@ -139,7 +139,7 @@ teardown() {
     assert_success
   fi
 
-  run /bin/bash -c "dokku config:set $TEST_APP SECRET_KEY_BASE=derp OTP_SECRET=1234"
+  run /bin/bash -c "dokku config:set $TEST_APP SECRET_KEY_BASE=derp OTP_SECRET=1234 LOCAL_DOMAIN=dokku.me"
   echo "output: $output"
   echo "status: $status"
   assert_success