Align plugins filtering for 'fuel2 graph list' command

Change-Id: Iba533f795f78bcd74d5989eff9ed9342c66d05b0
Closes-Bug: 1638605
(cherry picked from commit 57bbc76a78)

fuelclient/commands/graph.py

@@ -329,7 +329,7 @@ class GraphList(base.BaseListCommand):
             '--plugins',
             dest='filters',
             action='append_const',
-            const='plugins',
+            const='plugin',
             help='Include plugins-specific graphs'
         )
         parser.add_argument(

fuelclient/tests/unit/v2/cli/test_deployment_graph.py

@@ -354,9 +354,9 @@ class TestGraphActions(test_engine.BaseCLITest):
             self.exec_command('graph list')
 
             self.m_client.list.assert_has_calls([
-                mock.call(env_id=1, filters=['release', 'plugins', 'cluster']),
+                mock.call(env_id=1, filters=['release', 'plugin', 'cluster']),
                 mock.call(env_id=None, filters=['release']),
-                mock.call(env_id=None, filters=['plugins']),
+                mock.call(env_id=None, filters=['plugin']),
                 mock.call(env_id=None, filters=['cluster']),
                 mock.call(env_id=None, filters=None)
             ])

fuelclient/tests/unit/v2/lib/test_deployment_graph.py

@@ -274,7 +274,7 @@ class TestDeploymentGraphFacade(test_api.BaseLibTest):
 
         self.assertItemsEqual(
             enabled_plugin_graphs,
-            self.client.list(env_id, filters=['plugins'])
+            self.client.list(env_id, filters=['plugin'])
         )
 
         self.assertItemsEqual(

fuelclient/v1/graph.py

@@ -264,7 +264,7 @@ class GraphClient(base_v1.BaseV1Client):
         # we cannot use dict here, because order is important
         handlers = (
             ('release', self.get_env_release_graphs_list),
-            ('plugins', self.get_env_plugins_graphs_list),
+            ('plugin', self.get_env_plugins_graphs_list),
             ('cluster', self.get_env_cluster_graphs_list)
         )