Add warning filter

Author: snbianco

setup.cfg

@@ -87,6 +87,8 @@ filterwarnings =
     ignore:The upstream SHA API has been changed:UserWarning
 # CDMS triggers this, but we don't use it directly
     ignore: The 'strip_cdata' option of HTMLParser:DeprecationWarning
+# Datetime deprecation warnings
+    ignore::DeprecationWarning:datetime\.datetime
 
 markers =
     bigdata: marks tests that are expected to trigger a large download (deselect with '-m "not bigdata"')