Store/restore Server from a dict with credentials

The patch adds two methods to Server class to get a dict with
credentials from instance of its class and restore an instance from
credentials. LxcProvider requires reconstruction of the Server objects
for destruction of resources.

blueprint db-resource-track

Change-Id: I2f9ca4a1c49477d665ba02ff0736c21a7557e12a

rally/serverprovider/provider.py

@@ -34,6 +34,20 @@ class Server(utils.ImmutableMixin):
         self.ssh = sshutils.SSH(ip, user)
         super(Server, self).__init__()
 
+    def get_credentials(self):
+        return {
+            'uuid': self.uuid,
+            'ip': self.ip,
+            'user': self.user,
+            'key': self.key,
+            'password': self.password,
+        }
+
+    @classmethod
+    def from_credentials(cls, creds):
+        return cls(creds['uuid'], creds['ip'], creds['user'], creds['key'],
+                   password=creds['password'])
+
 
 class ImageDTO(utils.ImmutableMixin):
     """Represent information about created image.

tests/serverprovider/test_provider.py

@@ -83,15 +83,24 @@ class ProviderTestCase(test.TestCase):
 
 
 class ServerTestCase(test.TestCase):
+    def setUp(self):
+        super(ServerTestCase, self).setUp()
+        self.vals = ['uuid', '192.168.1.1', 'admin', 'some_key', 'pwd']
+        self.keys = ['uuid', 'ip', 'user', 'key', 'password']
 
     def test_init_server_dto(self):
-        vals = ['uuid', '192.168.1.1', 'admin', 'some_key', 'pwd']
-        keys = ['uuid', 'ip', 'user', 'key', 'password']
-        server = serverprovider.Server(*vals)
-        for k, v in dict(zip(keys, vals)).iteritems():
+        server = serverprovider.Server(*self.vals)
+        for k, v in dict(zip(self.keys, self.vals)).iteritems():
             self.assertEqual(getattr(server, k), v)
         self.assertIsInstance(server.ssh, sshutils.SSH)
 
+    def test_credentials(self):
+        server_one = serverprovider.Server(*self.vals)
+        creds = server_one.get_credentials()
+        server_two = serverprovider.Server.from_credentials(creds)
+        for k in self.keys:
+            self.assertEqual(getattr(server_one, k), getattr(server_two, k))
+
 
 class ImageDTOTestCase(test.TestCase):
     def test_init_image_dto(self):