tap-test: fix typo and actually create .test marker

We have this chunk in tap-test:

    if test -f ${test_tmpdir}/.test; then
      rm "${tempdir}" -rf
    fi

But (1) we were never actually touching `.test` and (2), we were
checking in `test_tmpdir` instead of `tmpdir`. This meant that the test
dirs were never actually cleaned up.

Create the marker file and make sure we rm the right dir. Also re-indent
to remove tabs.

Closes: #854
Approved by: cgwalters

buildutil/tap-test

@@ -1,19 +1,21 @@
 #! /bin/bash
+set -euo pipefail
 
 # run a GTest in tap mode. The test binary is passed as $1
 
 srcd=$(cd $(dirname $1) && pwd)
 bn=$(basename $1)
-tempdir=$(mktemp -d)
+test_tmpdir=$(mktemp -d)
 function cleanup () {
   if test -z "${TEST_SKIP_CLEANUP:-}"; then
     if test -f ${test_tmpdir}/.test; then
-            rm "${tempdir}" -rf
+      rm "${test_tmpdir}" -rf
     fi
   else
     echo "Skipping cleanup of ${test_tmpdir}"
   fi
 }
 trap cleanup EXIT
-cd ${tempdir}
+cd ${test_tmpdir}
+touch .test
 ${srcd}/${bn} -k --tap