Make spec_test idempotent (elastic#16392)

The previous implementation was actually saving the content over existing
spec files. So everytime that you ran the test the files would have be
modified and you had to ignore them on commit.

This commit move the generated file into a temporary directory.

x-pack/agent/pkg/agent/program/spec_test.go

@@ -6,6 +6,8 @@ package program
 
 import (
 	"io/ioutil"
+	"os"
+	"path/filepath"
 	"regexp"
 	"strings"
 	"testing"
@@ -100,9 +102,14 @@ when: 1 == 1
 }
 
 func TestExport(t *testing.T) {
+	dir, err := ioutil.TempDir("", "test_export")
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
 	for _, spec := range Supported {
 		b, err := yaml.Marshal(spec)
 		require.NoError(t, err)
-		ioutil.WriteFile("../../../spec/"+strings.ToLower(spec.Name)+".yml", b, 0666)
+		err = ioutil.WriteFile(filepath.Join(dir, strings.ToLower(spec.Name)+".yml"), b, 0666)
+		require.NoError(t, err)
 	}
 }