test/zdtm: use flock64 instead of flock

For 32-bit fcntl() Glibc function calls sys_fcntl64(), which
needs struct flock64, otherwise the kernel gets a wrong struct.
For 64-bit, it's all the same.

Also unset errno before fcntl() and check return value of the call.

Cc: Qiang Huang <h.huangqiang@huawei.com>
Cc: Begunkov Pavel <asml.silence@gmail.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
travis-ci: success for test/zdtm: use flock64 instead of flock
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>