reno has an open TODO [1] to sort branches by something other than
alphabetical order. Unfortunately we're hitting this here since heat
previously had a 'vN-branch' branch naming scheme, and reno thinks those
branches are newer than e.g. 'stable/train'.
The solution is to just be stricter in how we select our branches and
tags, preventing those with hyphens in them from being accepted.
[1] https://github.com/openstack/reno/blob/3.0.0/reno/scanner.py#L850-L852
Change-Id: I75841d0dcb8e69214b7e96cf04f8b095da4d81d2
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>