Most of wic functionality doesn't depend on .wicenv file,
so it's better to generate it only in test_image_env
test case where it's used.
(From OE-Core rev: caf9b41e1db7b565ef977200195d57b385127de9)
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>