updated auto.yaml with 6.0.0 tagging and release-notes URL

updated auto.yaml with 6.0.0 tagging and release-notes URL

patch 2:
fixed leading space issue

patch 3:
cherry-picked commits that were merged in master since initial
stable/fraser branch; applied to Auto stable/fraser; submitted;
used resulting new stable/fraser SHA1 as the SHA1 for
Auto release 6.0.0 (3a957...); didn't change original
stable/fraser SHA1 as Auto branch stable/fraser (5c811...);
branches: https://gerrit.opnfv.org/gerrit/#/admin/projects/auto,branches
changes: https://gerrit.opnfv.org/gerrit/#/q/project:auto

Change-Id: I39c6acaeacc749b17489553e2af52e06902d2828
Signed-off-by: Gerard Damm <gerard.damm@wipro.com>
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>