tests: drop mktemp(1) flags for better compatibility
tests: drop mktemp(1) flags for better compatibility

$ mktemp --tmpdir tmp.XXXXXXXXXX.yuv
mktemp: illegal option -- -
usage: mktemp [-d] [-q] [-t prefix] [-u] template ...
       mktemp [-d] [-q] [-u] -t prefix
$ gmktemp --tmpdir tmp.XXXXXXXXXX.yuv
/tmp/tmp.ddQTBn4XmE.yuv

$ mktemp -t tmp.XXXXXXXXXX.yuv
/tmp/tmp.XXXXXXXXXX.yuv.SYYNp8Ki
$ gmktemp -t tmp.XXXXXXXXXX.yuv
/tmp/tmp.2ena2nKgv5.yuv

$ mktemp -t yuv
/tmp/yuv.rX2UAbax
$ gmktemp -t yuv
gmktemp: too few X's in template ‘yuv’

ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar,ultravideo/kvazaar