Neutron v2 API: fix get_floating_ip_pools

Commit 7254f9b9dfbadadeb3aeda5d02bf37bfeb65e72d changed this method
in nova.network.api in a way that it now returns simply a list of
floating ip pool names, rather a list of dicts in the form

{'name': 'pool_name'}

The implementation of get_floating_ip_pools for neutron needs to
be changed accordingly. Otherwise nova's floating ip extension
will return a dict as floating ip pool names when neutron is enabled.

Change-Id: I27001c9f17dad4dc4ca8cd032e689736553d8225
Closes-Bug: #1355882
Merge "Neutron v2 API: fix get_floating_ip_pools"