Set default for disabled and update error message

Author: hush-hush

CHANGELOG.md

@@ -1,6 +1,9 @@
 CHANGELOG
 =========
 
+# 2.1.0 / 2017-12-26
+- [FEATURE] Disable callback if required python packages aren't installed. See [#28][] (thanks to @dobber)
+
 # 2.0.0 / 2017-12-12
 - [FEATURE] Add support for getting api_key from hostvars and thus from vault. See [#25][]
 - [BREAKING CHANGE] Drop support for ansible <2.0

datadog_callback.py

@@ -18,7 +18,9 @@ class CallbackModule(CallbackBase):
     def __init__(self):
         if not HAS_MODULES:
             self.disabled = True
-            print 'Datadog callback disabled.\nMake sure you call all required libraries.'
+            print 'Datadog callback disabled.\nMake sure you call all required libraries: "datadog" and "yaml".'
+        else:
+            self.disabled = False
 
         self._playbook_name = None
         self._start_time = time.time()