HPCC-9126 DFU Workunits Refactor

Fixes HPCC-9126

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #4278 from GordonSmith/HPCC-9126

HPCC-9126 DFU Workunits Refactor

Reviewed-By: Richard Chapman <rchapman@hpccplatform.com>
Reviewed-By: Miguel Vazquez <miguel.vazquez@lexisnexis.com>