[core] fix bug in hints option for csv parser

Not every parser requires the 'hints' key, yet the csv parser was calling it
without a .get().  In the case of KV data, this would throw a KeyError.

stream_alert/parsers.py

@@ -248,7 +248,7 @@ def parse(self):
             - False if the data is not CSV or the columns do not match.
         """
         schema = self.schema
-        hints = self.options['hints']
+        hints = self.options.get('hints')
 
         hint_result = []
         csv_payloads = []