Plugins that build stuff in the pull phase cannot be cleaned

[Sergio Schvezov]

By design `clean -s build` was supposed to clear out all the built assets put in the part's `install` directory. Given that some plugins put """build""" during the pull phase and put stuff in the part's `install` directory, when cleaning the build step for it, the `install` directory for it would be wiped and with that, make building impossible as we would have missing assets brought in from the pull phase.