Add again the check for valid credentials

As our check is more strict that the one provided in googlemaps library.

server/lib/python/cartodb_services/cartodb_services/google/client_factory.py

@@ -2,6 +2,8 @@
 # -*- coding: utf-8 -*-
 
 import googlemaps
+import base64
+from exceptions import InvalidGoogleCredentials
 
 class GoogleMapsClientFactory():
     clients = {}
@@ -10,8 +12,25 @@ class GoogleMapsClientFactory():
     def get(cls, client_id, client_secret):
         client = cls.clients.get(client_id)
         if not client:
+            cls.assert_valid_crendentials(client_secret)
             client = googlemaps.Client(
                 client_id=client_id,
                 client_secret=client_secret)
             cls.clients[client_id] = client
         return client
+
+    @classmethod
+    def assert_valid_crendentials(cls, client_secret):
+        if not cls.valid_credentials(client_secret):
+            raise InvalidGoogleCredentials
+
+    @staticmethod
+    def valid_credentials(client_secret):
+        try:
+            # Only fails if the string dont have a correct padding for b64
+            # but this way we could provide a more clear error than
+            # TypeError: Incorrect padding
+            base64.b64decode(client_secret)
+            return True
+        except TypeError:
+            return False

server/lib/python/cartodb_services/cartodb_services/google/geocoder.py

@@ -1,10 +1,9 @@
 #!/usr/local/bin/python
 # -*- coding: utf-8 -*-
 
-import base64
 import googlemaps
 
-from exceptions import MalformedResult, InvalidGoogleCredentials
+from exceptions import MalformedResult
 from client_factory import GoogleMapsClientFactory