Make large-ops test boot a group of instances 3 times

large-ops previously just booted large_ops_number of instances
concurrently. In this case we are testing an 'empty' cloud, we also want
to see if things work with a bunch of servers already running.

Change-Id: I646398bb3d3ba9b81b0f6bf24644c7cd435a7b4c
diff --git a/tempest/scenario/test_large_ops.py b/tempest/scenario/test_large_ops.py
index b7a30f8..0210c56 100644
--- a/tempest/scenario/test_large_ops.py
+++ b/tempest/scenario/test_large_ops.py
@@ -31,7 +31,7 @@
     Test large operations.
 
     This test below:
-    * Spin up multiple instances in one nova call
+    * Spin up multiple instances in one nova call, and repeat three times
     * as a regular user
     * TODO: same thing for cinder
 
@@ -69,3 +69,5 @@
             return
         self.glance_image_create()
         self.nova_boot()
+        self.nova_boot()
+        self.nova_boot()