openssh_cert - Adding regenerate option (#256)

* Initial commit

* Fixing unit tests

* More unit fixes

* Adding changelog fragment

* Minor refactor in Certificate.generate()

* Addressing option case-sensitivity and directive overrides

* Renaming idempotency to regenerate

* updating changelog

* Minor refactoring of default options

* Cleaning up with inline functions

* Fixing false failures when regenerate=fail and improving clarity

* Applying second round of review suggestions

* adding helper for safe atomic moves

plugins/module_utils/openssh/backends/common.py

@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright: (c) 2021, Andrew Pantuso (@ajpantuso) <ajpantuso@gmail.com>
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+import os
+
+
+def restore_on_failure(f):
+    def backup_and_restore(module, path, *args, **kwargs):
+        backup_file = module.backup_local(path) if os.path.exists(path) else None
+
+        try:
+            f(module, path, *args, **kwargs)
+        except Exception:
+            if backup_file is not None:
+                module.atomic_move(backup_file, path)
+            raise
+        else:
+            module.add_cleanup_file(backup_file)
+
+    return backup_and_restore
+
+
+@restore_on_failure
+def safe_atomic_move(module, path, destination):
+    module.atomic_move(path, destination)