added the datadog package to the requirement

requirements.txt

@@ -12,6 +12,8 @@ python-simple-hipchat==0.2
 prettytable==0.7.2
 awscli==1.4.2
 requests
+datadog==0.8.0
+
 # Needed for the mongo_status module(playbooks/library/mongo_status)
 pymongo==3.1