freebsd-update: for rollback, first create directories

rollback_files() tried to install files before creating the directories
for those files. In some cases this is due to special handling to
install certain classes of files earlier than others.

Just create all directories up front when performing rollback.

PR: 273950
Reviewed by: dim
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D42020