Add chassis lowers the case of added machines

[Lee Trager]

When any chassis is added the rack controller calls coerce_to_valid_hostname on the discovered hostname. This automatically lowers the case. Hostnames are case insensitive and MAAS allows you to manually create a hostname with upper case. Lowering the case causes there to be a mismatch between what is in the chassis vs what MAAS has.

When adding machines with add-chassis the case should be preserved.