Add an extra check for google credentials

If the user has a wrong base64 padded secret key the googlemaps
python library is returning "TypeError: Incorrect padding" which
is very hard to understand. So now we check if the secret key is
a valid base64 string

server/lib/python/cartodb_services/setup.py

@@ -10,7 +10,7 @@ from setuptools import setup, find_packages
 setup(
     name='cartodb_services',
 
-    version='0.15.0',
+    version='0.15.1',
 
     description='CartoDB Services API Python Library',