When downloadfilename is specified, it is used to fetch from premirror.
So fix the test cases accordingly.
(Bitbake rev: 3b4d2e3b5024324058360a2a28f33c34114218d0)
Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>