refactor: use LogFailWithError to allow a unified exit code for golang commands when the app is missing

plugins/common/common.go

@@ -515,10 +515,17 @@ func isValidAppNameOld(appName string) error {
 	return errors.New("App name must begin with lowercase alphanumeric character, and cannot include uppercase characters, or colons")
 }
 
+// AppDoesNotExist wraps error to include the app name
+// and is used to distinguish between a normal error and an error
+// where the app is missing
 type AppDoesNotExist struct {
 	appName string
 }
 
+func (err *AppDoesNotExist) ExitCode() int {
+	return 20
+}
+
 func (err *AppDoesNotExist) Error() string {
 	return fmt.Sprintf("App %s does not exist", err.appName)
 }