test: No need to git clean before running tup

Signed-off-by: Lewis Marshall <lewis@lmars.net>
Merge pull request #377 from flynn/remove-git-clean

test: No need to git clean before running tup
util/release: Support custom Docker image repository

Signed-off-by: Lewis Marshall <lewis@lmars.net>
util/release: Support a custom Docker registry

Signed-off-by: Lewis Marshall <lewis@lmars.net>