Fixed single quoted docstring

As per the docsctring standard, triple double-quoted
should be used for docstrings.

Changed single quoted docstring to double-quoted.

Closes-Bug: 1483556
Change-Id: I0633498fc353f0148a9dc7c9198c74e6f75244c0
diff --git a/tempest/api/baremetal/admin/test_nodes.py b/tempest/api/baremetal/admin/test_nodes.py
index 4830dcd..b6dee18 100644
--- a/tempest/api/baremetal/admin/test_nodes.py
+++ b/tempest/api/baremetal/admin/test_nodes.py
@@ -20,7 +20,7 @@
 
 
 class TestNodes(base.BaseBaremetalTest):
-    '''Tests for baremetal nodes.'''
+    """Tests for baremetal nodes."""
 
     def setUp(self):
         super(TestNodes, self).setUp()