Ignore old 'vN-branch' tags when scanning for release notes

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 <[email protected]>

Author: stephenfin

.gitignore

@@ -35,6 +35,7 @@ doc/source/_static/heat.policy.yaml.sample
 
 # Files created by releasenotes build
 releasenotes/build
+releasenotes/notes/reno.cache
 
 # sample config included in docs
 doc/source/_static/heat.conf.sample

releasenotes/config.yaml

@@ -0,0 +1,4 @@
+---
+branch_name_re: '^stable/\w+$'
+release_tag_re: '((?:[\d.ab]|rc)+)'
+closed_branch_tag_re: '^(\w+)-eol$'