Clean up temp files more thoroughly after testing. (#7815)

Our test cases spew a lot of files and directories around $TMPDIR.  Make more
thorough use of the testing package's TempDir methods to ensure these are
cleaned up.

In a few cases, this required plumbing test contexts through existing helper
code. In a couple places an explicit path was required, to work around cases
where we do global setup during a TestMain function. Those cases probably
deserve more thorough cleansing (preferably with fire), but for now I have just
worked around it to keep focused on the cleanup.

internal/mempool/mempool_test.go

@@ -82,7 +82,7 @@ func setup(ctx context.Context, t testing.TB, cacheSize int, options ...TxMempoo
 	cc := abciclient.NewLocalCreator(app)
 	logger := log.TestingLogger()
 
-	cfg, err := config.ResetTestRoot(strings.ReplaceAll(t.Name(), "/", "|"))
+	cfg, err := config.ResetTestRoot(t.TempDir(), strings.ReplaceAll(t.Name(), "/", "|"))
 	require.NoError(t, err)
 	cfg.Mempool.CacheSize = cacheSize
 	appConnMem, err := cc(logger)

internal/mempool/reactor_test.go

@@ -41,7 +41,7 @@ type reactorTestSuite struct {
 func setupReactors(ctx context.Context, t *testing.T, numNodes int, chBuf uint) *reactorTestSuite {
 	t.Helper()
 
-	cfg, err := config.ResetTestRoot(strings.ReplaceAll(t.Name(), "/", "|"))
+	cfg, err := config.ResetTestRoot(t.TempDir(), strings.ReplaceAll(t.Name(), "/", "|"))
 	require.NoError(t, err)
 	t.Cleanup(func() { os.RemoveAll(cfg.RootDir) })