All hists test cases forget to reset err after using it to hold an
error code. If error occure in setup_fake_machine() it incorrectly
return TEST_OK.

This patch fixes it.
Suggested-and-Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1452520124-2073-13-git-send-email-wangnan0@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>