fix issues with build-docker-image

- fix typo in --namespace option

    build-docker-image had a missing '$' in the code that handled the
    --namespace option.

- force builds to kollaglue namespace with 'latest' tag to use
  the --release flag

- build IMAGE after config and options processing to permit overriding
  PREFIX in .buildconf

Change-Id: Icf70b33080ef19643f133f2b6f60087c524bd4fb
Merge "fix issues with build-docker-image"