Silence CryptogrpahyDeprecationWarning in metadata module

lib/galaxy/metadata/set_metadata.py

@@ -15,6 +15,12 @@
 import os
 import sys
 import traceback
+import warnings
+
+# Warning on stderr will cause some jobs to be failed.
+# This silences deprecation warnings in the cryptography module.
+if sys.version_info.major <= 3 and sys.version_info.minor < 6:
+    warnings.filterwarnings("ignore", module='CryptographyDeprecationWarning')
 
 from six.moves import cPickle
 from sqlalchemy.orm import clear_mappers