tap-test: create tmpdir in /var/tmp

So that we can use xattrs.

Closes: #854
Approved by: cgwalters

buildutil/tap-test

@@ -2,10 +2,11 @@
 set -euo pipefail
 
 # run a GTest in tap mode. The test binary is passed as $1
+# use /var/tmp so we can use xattrs in case /tmp is on tmpfs
 
 srcd=$(cd $(dirname $1) && pwd)
 bn=$(basename $1)
-test_tmpdir=$(mktemp -d)
+test_tmpdir=$(mktemp -d /var/tmp/tap-test.XXXXXX)
 function cleanup () {
   if test -z "${TEST_SKIP_CLEANUP:-}"; then
     if test -f ${test_tmpdir}/.test; then