Fixed UnexpectedValueException

When adding custom roles which implement
Zend\Permissions\Rbac\RoleInterface, an UnexpectedValueException is
thrown due to missing RecursiveIterator implementation.

Fixed this exception by improving the hasChildren() implementation in
Zend\Permissions\Rbac\AbstractIterator
Fixed cs violation

Removed the leading slash from interface name string passed to
getMockForAbstractClass().
Fixed incorrect return annotation

The @return annotation for Zend\Permissions\Rbac\Rbac::addRole() is
incorrect. This method returns $this and not the rule instance.
Merge pull request #4210 from tux-rampage/rbac-issue

Fixed failure when implementing custom rbac roles
[#4210] CS fix

- docblock can simply refer to "self"
Merge branch 'hotfix/4210'

Close #4210