crash_sender: use more random tmpdir

The POSIX spec often requires 6 X's in temp paths.  Change the code
to use that rather than the non-standard 4.

BUG=chromium:275910
TEST=`cbuildbot {arm,amd64,x86}-generic-full` works
TEST=`crash_sender` on board works

Change-Id: I97f5959afcb9f60dfd379d517904d5bbf5c502e3
Reviewed-on: https://chromium-review.googlesource.com/169680
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
1 file changed
tree: d73898e76bcab4959a6ca63aa8a1cadb2d322069
  1. crash_reporter/