UTIL: Use alternative way for detecting PyErr_NewExceptionWithDoc
    
    Function PyErr_NewExceptionWithDoc was added in python 2.7.0
    and we use fallback implementation for older versions of python.
    
    Previously, we used detection of PyErr_NewExceptionWithDoc at configure
    time; but it does not work well in case of python2.6 and python3.x
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3656
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>