Make the Neutron l3 plugin use the subnetpools
Make the Neutron l3 plugin use the subnetpools

The plugin creates subnetpools but does not use them when creating the
default subnets. It uses CIDR values that overlap with the
default pools. Change this to use the subnetpools.

Change-Id: I6171c13507e420f146801d323cb1011be36c1e8c
Closes-bug: 1613717

nawawi/openstack,nawawi/openstack,noironetworks/devstack,noironetworks/devstack,group-policy/devstack,richliu/devstack,bswartz/devstack,dtroyer/devstack,bswartz/devstack,openstack-dev/devstack,group-policy/devstack,openstack-dev/devstack,dtroyer/devstack,richliu/devstack