[testlib] consider rset for template / view selection (closes #2447183) The original code did something like: kwargs['rset'] = rset viewfunc = lambda **k: viewsreg.main_template(req, template, **kwargs) kwargs.pop('rset') return self._test_view(viewfunc, view, template, kwargs) meaning that by the time ``viewfunc`` (i.e. the lambda function) is called, ``rset`` was popped from ``kwargs`` and had no chance to be passed to ``main_template``.