The commands that do not require authentication sometimes still need
to call ClientManager.is_network_endpoint_enabled() to see if Neutron
is available. Optimize the paths a bit to skip auth when it is not
necessary; the upshot is Neutron will be assumed in these cases now.
This gets a LOT cleaner when it appears is a future osc-lib.
Change-Id: Ifaddc57dfa192bde04d0482e2cdcce111313a22a