Nodestate API test for power state set

This patch implements Nodestate API tests, to set the power state of
the node for the following power states -
1. power on
2. rebooting
3. power off

Change-Id: Icbb2719ffae772878f183c0c77c1e9d9028655c1
diff --git a/tempest/services/baremetal/base.py b/tempest/services/baremetal/base.py
index 2af287f..321b08b 100644
--- a/tempest/services/baremetal/base.py
+++ b/tempest/services/baremetal/base.py
@@ -199,3 +199,14 @@
 
         """
         return self._list_request(version, permanent=True)
+
+    def _put_request(self, resource, put_object):
+        """
+        Update specified object with JSON-patch.
+
+        """
+        uri = self._get_uri(resource)
+        put_body = json.dumps(put_object)
+
+        resp, body = self.put(uri, body=put_body)
+        return resp, body