♿ Fix logging when ran through flask run

This assures applications ran via ``flask run`` will grab app, but
tests or anything importing will not implicitly create app (and hook
into pymongo monitoring).

Without this, flask would implicitly use create_app to start Flask,
which won't properly bind pymongo.

examples/flask_todo/app.py

@@ -1,6 +1,8 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+import os
+
 from flask import Flask
 from flask_mongoengine import MongoEngine
 
@@ -74,4 +76,9 @@ def index():
     return app
 
 
-app = create_app()
+if __name__ == '__main__' or os.getenv('FLASK_RUN_FROM_CLI') == 'true':
+    """
+    For some reason falling back onto create_app when running ``flask run`` doesn't
+    bind pymongo.monitoring. See also: http://flask.pocoo.org/docs/1.0/cli/.
+    """
+    app = create_app()