Make pymongo backend testing PyMongo 3 compatible

Fix deprecation warning that only requires PyMongo 3.0.0 in test_model.

flask_admin/tests/pymongo/__init__.py

-import pymongo
+from pymongo import MongoClient
 
 from flask import Flask
 from flask_admin import Admin
@@ -9,8 +9,8 @@ def setup():
     app.config['SECRET_KEY'] = '1'
     app.config['CSRF_ENABLED'] = False
 
-    conn = pymongo.Connection()
-    db = conn.tests
+    client = MongoClient()
+    db = client.tests
 
     admin = Admin(app)
 

flask_admin/tests/pymongo/test_basic.py

@@ -26,7 +26,7 @@ def test_model():
     admin.add_view(view)
 
     # Drop existing data (if any)
-    db.test.remove()
+    db.test.delete_many({})
 
     eq_(view.name, 'Test')
     eq_(view.endpoint, 'testview')