Set log level for catalog metadata validation ERR

Invalid values for THREDDS Catalog Metadata are not
all that importiant for the end users to see. This
commit sets the log level to ERROR instead of
WARNING.

siphon/metadata.py

@@ -11,7 +11,7 @@
 import logging
 
 log = logging.getLogger(__name__)
-log.setLevel(logging.WARNING)
+log.setLevel(logging.ERROR)
 
 
 class _SimpleTypes(object):