This option indicates the number of (available) compute hosts in the
deployment, and will be used by tests that require all their instances
landing on the same host (ie, a single-compute deployment). The
default value is a childish large number to make sure that tests that
need a single node are skipped unless max_compute_nodes is set.
Change-Id: Id274baeb13ce87783e35daff74bf4cfe67554900