linter: (1/2) enable errcheck (#5064)

## Description

partially cleanup in preparation for errcheck

i ignored a bunch of defer errors in tests but with the update to go 1.14 we can use `t.Cleanup(func() { if err := <>; err != nil {..}}` to cover those errors, I will do this in pr number two of enabling errcheck.

ref #5059

config/toml_test.go

@@ -25,7 +25,7 @@ func TestEnsureRoot(t *testing.T) {
 	// setup temp dir for test
 	tmpDir, err := ioutil.TempDir("", "config-test")
 	require.Nil(err)
-	defer os.RemoveAll(tmpDir) // nolint: errcheck
+	defer os.RemoveAll(tmpDir)
 
 	// create root dir
 	EnsureRoot(tmpDir)