Configure some tempest settings depending on if running multitenant vs
flat-network.
Add setting of [compute]/fixed_network_name for the flat-network case,
as this is required to run tempest "smoke" test.
Starting with the Newton release, multitenancy is available with
Ironic. This patch sets tempest auth.create_isolated_networks=False and
network.shared_physical_network=True only when Ironic is deployed for
a flat-network.
Partial-Bug: #1646640
Change-Id: I9807014b739b7364502d403e7ce72763f5ea698a
88171fcebd