add TEMPEST_LARGE_OPS_NUMBER to option

The tempest scenario.large_ops test tries to catch any performance issues
when running large numbers of operations at once, in this case launching
instances.

Set to 0 by default, to maintain the current default, but add this as an
option so this can be set via devstacks localrc.

Part of regression test for bug 1199433

Change-Id: I459717b849f9b6d180a7956c0ff470cefe7c1ff6
diff --git a/lib/tempest b/lib/tempest
index 0d4f370..50289b6 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -282,6 +282,9 @@
     # Scenario
     iniset $TEMPEST_CONF scenario img_dir "$FILES/images/cirros-0.3.1-x86_64-uec"
 
+    # Large Ops Number
+    iniset $TEMPEST_CONF scenario large_ops_number ${TEMPEST_LARGE_OPS_NUMBER:-0}
+
     # Volume
     CINDER_MULTI_LVM_BACKEND=$(trueorfalse False $CINDER_MULTI_LVM_BACKEND)
     if [ $CINDER_MULTI_LVM_BACKEND == "True" ]; then