reno doesn't currently handle missing branches so we need
to use the liberty-eol tag to fix the release note job in
the gate now that origin/stable/liberty is gone.
reno will eventually check for the -eol tag when a stable
branch isn't found in:
I41ab682f081e7fd39ea534b7e2180c2109ca34ef
Change-Id: Ie54f69f5c1f91a3781c876f035fe9ed838e11c08
4a237c02e4