Setting nova::metadata::dhcp_domain will no longer work unless nova::metadata
is included.
Since I07caa3185427b48e6e7d60965fa3e6157457018c we no longer include
nova::metadata on computes.
So we must now set nova::dhcp_domain in nova-base instead of relying on the
deprecated nova::metadata::dhcp_domain param.
Closes-bug: #1905418
Depends-on: I98fe83e0c245388944529cd19b5e2bbed134e855
Change-Id: Iaf7823ea8d456008c1f4a3d7631657faa65eb6d3