At the moment, if live_migration_inbound_addr is not defined it
will default to the hostname of the hypervisor which requires
DNS in order to work properly.
DNS can be complicated and it is possible that an environment
might not have it, so it makes sense to default to grabbing the
default route interface to do live migrations over in order
to allow live migrations when DNS is not setup.
Change-Id: I10eb63fc64d7cd34ef89df529637b1e81951e38c
8f0a154138