Add entities.PartitionTable.update()

Added ```entities.PartitionTable.update()```, as it's needed for SatelliteQE/robottelo#2502.
Part of SatelliteQE#111.

nailgun/entities.py

@@ -2759,7 +2759,11 @@ def repository_sets_available_repositories(self, reposet_id):
 
 
 class PartitionTable(
-        Entity, EntityCreateMixin, EntityDeleteMixin, EntityReadMixin):
+        Entity,
+        EntityCreateMixin,
+        EntityDeleteMixin,
+        EntityReadMixin,
+        EntityUpdateMixin):
     """A representation of a Partition Table entity."""
 
     def __init__(self, server_config=None, **kwargs):
@@ -2774,6 +2778,17 @@ def __init__(self, server_config=None, **kwargs):
         self._meta = {'api_path': 'api/v2/ptables', 'server_modes': ('sat')}
         super(PartitionTable, self).__init__(server_config, **kwargs)
 
+    def update(self, fields=None):
+        """Fetch a complete set of attributes for this entity."""
+        self.update_json(fields)
+        return self.read()
+
+    def update_payload(self, fields=None):
+        """Wrap submitted data within an extra dict."""
+        return {
+            u'ptable': super(PartitionTable, self).update_payload(fields)
+        }
+
 
 class PuppetClass(
         Entity, EntityCreateMixin, EntityDeleteMixin, EntityReadMixin):

tests/test_entities.py

@@ -846,6 +846,7 @@ def test_generic(self):
             entities.HostGroup(self.cfg),
             entities.Location(self.cfg),
             entities.Organization(self.cfg),
+            entities.PartitionTable(self.cfg),
             entities.User(self.cfg),
         )
         for entity in entities_:
@@ -893,6 +894,7 @@ def test_generic(self):
             (entities.HostGroup, {'hostgroup': {}}),
             (entities.Location, {'location': {}}),
             (entities.Organization, {'organization': {}}),
+            (entities.PartitionTable, {'ptable': {}}),
             (entities.User, {'user': {}}),
         ]
         for klass, response in class_response: