Process rootfs one at a time

[pombredanne]

In the root_filesystems.py pipeline in the step:

    @step
    def match_not_analyzed_to_system_packages(self):
        """
        Match not-yet-analyzed files to files already related to system packages.
        """
        rootfs.match_not_analyzed(
            self.project,
            reference_status="system-package",
            not_analyzed_status="",
        )
        self.next(self.match_not_analyzed_to_application_packages)

... we should consider doing it one rootfs at a time if there are several rootfs at once in the project e.g. for rfs in self.root_filesystems:...