DAPI-238 - add support for server_spread, allowing ops to change certain aspects
of allocation behaviour either by using the 'server_spread' attribute in a package,
or setting DAPI_DEFAULT_SPREAD to one of 'min-ram' (the default), 'min-owner', or
'random' in sapi. Be careful when changing from the default, it could affect
availability of space for large packages in the future.