devstack: Fix Keystone v3 configuration typo
devstack: Fix Keystone v3 configuration typo

When Keystone v3 is enabled, 'default' is the id, not the name,
of the domain created by devstack.

Change-Id: I244db7023cb3215dc6fe26d783c6338c8391a0f4

openstack/aodh,openstack/aodh