Increase host_subset_size for ironic

This patch increase host_subset_size when ironic is used to 999
to minimize race conditions.

Change-Id: I0874fe3b3628cb3e662ee01f24c4599247fdc82d
diff --git a/lib/nova_plugins/hypervisor-ironic b/lib/nova_plugins/hypervisor-ironic
index d59473c..062afb7 100644
--- a/lib/nova_plugins/hypervisor-ironic
+++ b/lib/nova_plugins/hypervisor-ironic
@@ -47,6 +47,8 @@
         iniset $NOVA_CONF filter_scheduler use_baremetal_filters True
     fi
 
+    iniset $NOVA_CONF filter_scheduler host_subset_size 999
+
     iniset $NOVA_CONF DEFAULT ram_allocation_ratio 1.0
     iniset $NOVA_CONF DEFAULT reserved_host_memory_mb 0
     # ironic section