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