test/system: Limit the scope of temporary files used by a single test

BATS_TMPDIR is the base directory used by Bats for all temporary files
and directories, and BATS_TEST_TMPDIR is unique to each test [1].  It's
better to limit the scope of the tests' temporary files as much as
possible to avoid unexpected collisions with Bats' own internal
temporary files.

[1] https://bats-core.readthedocs.io/en/stable/writing-tests.html

containers#1327

test/system/104-run.bats

@@ -166,11 +166,11 @@ teardown() {
 @test "run: 'sudo id' inside the default container" {
   create_default_container
 
-  output="$($TOOLBOX --verbose run sudo id 2>$BATS_TMPDIR/stderr)"
+  output="$($TOOLBOX --verbose run sudo id 2>$BATS_TEST_TMPDIR/stderr)"
   status="$?"
 
   echo "# stderr"
-  cat $BATS_TMPDIR/stderr
+  cat $BATS_TEST_TMPDIR/stderr
   echo "# stdout"
   echo $output
 

test/system/libs/helpers.bash

@@ -227,9 +227,9 @@ function _clean_docker_registry() {
 
 
 function build_image_without_name() {
-  echo -e "FROM scratch\n\nLABEL com.github.containers.toolbox=\"true\"" > "$BATS_TMPDIR"/Containerfile
+  echo -e "FROM scratch\n\nLABEL com.github.containers.toolbox=\"true\"" > "$BATS_TEST_TMPDIR"/Containerfile
 
-  run $PODMAN build "$BATS_TMPDIR"
+  run $PODMAN build "$BATS_TEST_TMPDIR"
 
   assert_success
   assert_line --index 0 --partial "FROM scratch"
@@ -239,7 +239,7 @@ function build_image_without_name() {
   last=$((${#lines[@]}-1))
   assert_line --index "$last" --regexp "^[a-f0-9]{64}$"
 
-  rm -f "$BATS_TMPDIR"/Containerfile
+  rm -f "$BATS_TEST_TMPDIR"/Containerfile
 
   echo "${lines[$last]}"
 }