InfoMixin obtains documentation from objects __doc__ properties.
In case of class based scenarios, __doc__ property is empty (
we decided to use docstrings of "run" method).
This patch adds new object property - _doc_source_, which should include
object from which docstings will be used.
Change-Id: I799222fe213b96a88110d6d2ebb5aa3fe2d8f153