Change impersonator check code
In MIT 1.15 we now have a native way to check for an impersonator,
implement the use of that function but still keep the fallback for
earlier krb5 versions that do not support this method for now.
Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Robbie Harwood <rharwood@redhat.com>
Merges: #172