We need to iterate over multiple manifests, and generally use the
outer_client.manifest for multi-manifest support. This refactors the
use of self.manifest into a chosen manifest.
Change-Id: I992f21d610c929675e99555ece9c38df4b635839
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/334699
Tested-by: LaMont Jones <lamontjones@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>