step support trait - return closure result to caller

Now steps doesn't return anything, but some steps can't be isolated. For example here are a step of test case, that creates a new user. The next step should login this user to system, but to get a reference to this user object from the first step we have to write a bit of magic:

```
$userDecoratorObject = null;
         
$this->executeStep(
   'Creating new user',
   function () use (&$userDecoratorObject) {
      $userDecoratorObject = $this->_getUserFactory()->createUser();
   }
);
```
instead of:

```
$userDecoratorObject = $this->executeStep(
   'Creating new user',
   function () {
      return $this->_getUserFactory()->createUser();
   }
);
```