Optimization and response status code update

In following test files response status code is not being checked -
1. test_api_discovery.py
2. test_chassis.py
3. test_nodes.py
4. test_ports.py

This patch adds checking for missing response status code in above.
Also it optimize codes of files.
Change-Id: I4bc5aa756508b533919c283ce18f641fec50b30e
diff --git a/tempest/api/baremetal/test_api_discovery.py b/tempest/api/baremetal/test_api_discovery.py
index e594b3e..bee10b9 100644
--- a/tempest/api/baremetal/test_api_discovery.py
+++ b/tempest/api/baremetal/test_api_discovery.py
@@ -20,6 +20,7 @@
     @test.attr(type='smoke')
     def test_api_versions(self):
         resp, descr = self.client.get_api_description()
+        self.assertEqual('200', resp['status'])
         expected_versions = ('v1',)
 
         versions = [version['id'] for version in descr['versions']]
@@ -30,6 +31,7 @@
     @test.attr(type='smoke')
     def test_default_version(self):
         resp, descr = self.client.get_api_description()
+        self.assertEqual('200', resp['status'])
         default_version = descr['default_version']
 
         self.assertEqual(default_version['id'], 'v1')
@@ -37,6 +39,7 @@
     @test.attr(type='smoke')
     def test_version_1_resources(self):
         resp, descr = self.client.get_version_description(version='v1')
+        self.assertEqual('200', resp['status'])
         expected_resources = ('nodes', 'chassis',
                               'ports', 'links', 'media_types')