Prepare Al SR2 release

Prepare the Aluminium SR2 release
( device model 7.1 support may be needed for flexgrid since manufacturer devices don't propose it with previous versions - it can be integrated with SR2)

This means to:

• cherry-pick related bug corrections from master
• update project version in poms
• update dependencies if needed (mostly odlparent versions)
  https://docs.opendaylight.org/projects/integration-distribution/en/stable-aluminium/platform-versions.html
• update others environment parameters e.g. for lighty.io and tox if needed (normally not)
• update release notes https://git.opendaylight.org/gerrit/c/docs/+/93588

Once that done, the release must be staged in Jenkins and then officially released using the self-service process

https://docs.opendaylight.org/en/stable-aluminium/release-process/project-release.html

This last task can only be performed when all upstreams dep are ready i.e. when all managed projects have been released (prevision date 10/30/2020).
The deadline is one week after all managed projects have been released.

Evaluation indicators:

• cherry-picks from master done
• magnesium stage release job OK in Jenkins
• tpce artifacts published on nexus