title: Offline mode in firebase_admin in python?
body: <p>I create my firebase connection like this:</p>
  
  <pre><code>cred = credentials.Certificate('firebase_admin.json')
  default_app = firebase_admin.initialize_app(cred, {
      'databaseURL': 'https://xxx.firebaseio.com'
  })
  </code></pre>
  
  <p>Now, something like this works well:</p>
  
  <pre><code>ref = db.reference('foo')
  ref.set('bar')
  </code></pre>
  
  <p>But the problem is when my script is running there's sometimes no internet connection. It only uses firebase to write, it's not reading anything. When it happens script hangs and crashes with exception:</p>
  
  <pre><code>  File "/usr/local/lib/python2.7/site-packages/firebase_admin-2.1.1-py2.7.egg/firebase_admin/db.py", line 174, in push
    File "/usr/local/lib/python2.7/site-packages/firebase_admin-2.1.1-py2.7.egg/firebase_admin/db.py", line 600, in request
    File "/usr/local/lib/python2.7/site-packages/firebase_admin-2.1.1-py2.7.egg/firebase_admin/db.py", line 635, in _do_request
  firebase_admin.db.ApiCallError: HTTPSConnectionPool(host='autogleam-3c89b.firebaseio.com', port=443): Max retries exceeded with url: /logs/123456789.json (Caused by NewConnectionError('&lt;urllib3.connection.VerifiedHTTPSConnection object at 0x103a69e90&gt;: Failed to establish a new connection: [Errno 51] Network is unreachable',))
  </code></pre>
  
  <p>It doesn't work, because each write command works synchronously. I'd like to have something like offline mode and asynchronous data write. So when there's no internet connection it'll just send it as soon as it'll available and script just continues to work. Is this possible with firebase_admin?</p>