Fix and simplify reboot stress test. Add new env stuff.

Added stress environment var for max_instances.
Added tempest var for log_level of rest_client.

Change-Id: Ia92536a547cdab4d2496bd9ba9067be3595b79cd

xxxxx

Change-Id: I8c2f499a41f74c2fe6fb08c80ab6fc31f6b93426
diff --git a/stress/config.py b/stress/config.py
index 0dce816..16972d8 100755
--- a/stress/config.py
+++ b/stress/config.py
@@ -46,3 +46,8 @@
     def controller(self):

         """Controller host"""

         return self.get("controller", None)

+

+    @property

+    def max_instances(self):

+        """Maximum number of instances to create during test"""

+        return self.get("max_instances", 16)