Add delay option to std.echo to emulate external lags.

Change-Id: Id177246996434d2ad1c111b0b7bf78664390045a
Signed-off-by: Oleg Ovcharuk <vgvoleg@gmail.com>

doc/source/user/wf_lang_v2.rst

@@ -1118,6 +1118,8 @@ Input parameters:
 
 -  **output** - Value of any type that needs to be returned as a result
    of the action. *Required*.
+-  **delay** - Float value that defines with what delay (in seconds)
+   the result should be returned. *Optional*.
 
 std.javascript
 ''''''''''''''

mistral/actions/std_actions.py

@@ -42,13 +42,24 @@ class EchoAction(actions.Action):
     stub.
     """
 
-    def __init__(self, output):
+    def __init__(self, output, delay=0):
         super(EchoAction, self).__init__()
 
         self.output = output
+        try:
+            self._delay = float(delay)
+            self._delay = 0 if self._delay < 0 else self._delay
+        except ValueError:
+            self._delay = 0
 
     def run(self, context):
-        LOG.info('Running echo action [output=%s]', self.output)
+        LOG.info(
+            'Running echo action [output=%s, delay=%s]',
+            self.output,
+            self._delay
+        )
+
+        time.sleep(self._delay)
 
         return self.output