Add large_ops scenario test

Try spinning up a specific number of instances (set via config) by using
the min_instances option. And make sure all instances go to active
state. Note since the number of instances a cloud can handle is cloud
specific this test is disabled by default.

This can be used in Devstack by using the 'VIRT_DRIVER=fake' option in
devstack.

Change-Id: I30c7d7d113053b47d6dffa6295ad6068810cad32
diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 12aa399..702aec2 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -336,6 +336,10 @@
 # ssh username for the image file
 ssh_user = cirros
 
+# specifies how many resources to request at once. Used for large operations
+# testing."
+large_ops_number = 0
+
 [cli]
 # Enable cli tests
 enabled = True