[ADD] base_external_system: Implement interface/adapter (#993)

* [ADD] base_external_system: Implement interface/adapter for external systems

* base_external_system: Fix OS model, add inherits, add validate

* base_external_system: Usability and private key pass

* base_external_system: Use contextmanager in adapter client

* base_external_system: Move contextmanager to interface

* base_external_system: Include contextmanager on adapter and system

* base_external_system: Unify client

* Use password widget for password field

* Add tests & security

* Fix lint

* Add plaintext note

base_external_system/tests/common.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 LasLabs Inc.
+# License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl).
+
+from contextlib import contextmanager
+from mock import MagicMock
+
+from odoo.tests.common import TransactionCase
+
+
+class Common(TransactionCase):
+
+    @contextmanager
+    def _mock_method(self, method_name, method_obj=None):
+        if method_obj is None:
+            method_obj = self.record
+        magic = MagicMock()
+        method_obj._patch_method(method_name, magic)
+        try:
+            yield magic
+        finally:
+            method_obj._revert_method(method_name)