Use minimum OS specific path.

This change ensures LoadConfig and LoadConfigDir report consistent paths to files and those paths use the appropriate path separator for the target OS. Note that LoadConfigDir constructs paths with filepath.Join, which calls filepath.Clean, which calls filepath.FromSlash.

command/agent/config_test.go

@@ -327,7 +327,7 @@ func TestConfig_LoadConfigsFileOrder(t *testing.T) {
 	config := config1.Merge(config2)
 
 	if !reflect.DeepEqual(config.Files, expected) {
-		t.Errorf("Loaded configs don't match\nExpected\n%+vGot\n%+v\n",
+		t.Errorf("Loaded configs don't match\nwant: %+v\n got: %+v\n",
 			expected, config.Files)
 	}
 }