bulk: add option to build repository & INDEX without building any packages #420
Description
Whenever a lengthy poudriere bulk build is cancelled without finishing, or if a bulk build was giving the -N flag, the system is left with a number of new packages which have been built but are not available in the package database.
Whilst this is good default behaviour, it would be nice to provide a flag to bulk to allow the operator to specify that no additional packages should be built, just create a repository and INDEX with those packages that have already been built.