verify rsa.Key object to prevent segfault

Author: stavxyz

chef/api.py

@@ -75,6 +75,8 @@ def __init__(self, url, key, client, version='0.10.8', headers={}):
         self.parsed_url = urlparse.urlparse(self.url)
         if not isinstance(key, Key):
             key = Key(key)
+        if not key.key:
+            raise ValueError("ChefAPI attribute 'key' was invalid.")
         self.key = key
         self.client = client
         self.version = version