Trim rally scenario sizes
Trim rally scenario sizes

During a normal run, the top three scenarios account for slightly
more than a half hour of runtime. Sample numbers:

Scenario                                    Load Duration Full Duration
NeutronNetworks.create_and_update_subnets       562.189   1,182.400
NeutronTrunks.create_and_list_trunk_subports    427.475    600.721
NeutronNetworks.create_and_list_ports           310.167    540.144

This patch reduces the resources created by each of the 3 by 75%. This
should save us an additional ~20 minutes during a normal gate run, which
should change our window for timeout from approximately a half hour on a
normal node to about 50 minutes.

This additional buffer should hopefully be enough to reduce the failure
rate for the rally job when it gets scheduled to a slow node.

Change-Id: I923b625f7dd3ebf794b6a9e097f5ed12ce446bb5

huntxu/neutron,noironetworks/neutron,mahak/neutron,eayunstack/neutron,mahak/neutron,noironetworks/neutron,mahak/neutron,huntxu/neutron,openstack/neutron,openstack/neutron,eayunstack/neutron,openstack/neutron