Fix breakage caused by mktemp on older macOS

Gives proper argument (-t prefix) to mktemp in order to make it
work properly including older macOS.
Although adding "-t prefix" will behave differently on linux and macOS,
but the purpose of making a temporary file is achieved.

Bug: 63790380
Bug: 112431532
Test: $ mk_qemu_image.sh $OUT/sparse_system.img
      $ mk_qemu_image.sh $OUT/raw_system.img
Test: Built on Mac and do the commands above

Change-Id: I999e7f97531752a376925987f525f0446e649f00
1 file changed