R1:3c19e5b133b7

Avoid warning in checking config classes in setup

Summary:
Current code emits warning for classes with constructors with parameters.
It also creates the objects which is bad if constructors do some actual work.

NOTE: http://svn.php.net/viewvc/phpdoc/en/trunk/reference/reflection/reflectionclass/issubclassof.xml?r1=324630&r2=324629

Test Plan:
Run setup with:

- correct classes
- not-existing class
- class with private constructor
- class not implementing the required class

Reviewers: epriestley…