As per the REST Networking API v2.0 (Subnet) docs, if subnets pools
are not specified, OpenStack networking automatically allocates pools
covering all IP addresses in the CIDR.
In custom vendor specific environments, subnets can be created without
allocation pools via UI due to which subnets will not have any existing
allocation pools. Under this scenario, module throws an
"IndexError: list index out of range" error.
Also, allow to add more allocation pools on top of existing allocation
pools.
Change-Id: Ib8becf5e958f1bc8e5c9fd76f1722536bf1c9f1a