Fix result of HTTP action

 * Fixed HTTPAction result: To use expressions we need to
   transform any action result to some expressions-readable
   structure, e.g. dict. In case of HTTPActions we expose
   status, content and headers. For example, if we recieved
   response - {"server": "info" {"id": "some_id"}} we can
   address to property 'id' using expression '$.content.server.id'
 * Unit test

Change-Id: I9ecf4dc01f1ae084e27b29f46507c65fba9a6692