Update section with links to backport/RC potential bugs
Update section with links to backport/RC potential bugs

In this section there were only links to 3 stale branches.
Now it describes how link to Launchpad's page with
links to current stable branches can be build.

Change-Id: I721dfbb7e907eb1f4bac0fdb4f6fe35dc447dee1

openstack/neutron,noironetworks/neutron,mahak/neutron,mahak/neutron,eayunstack/neutron,openstack/neutron,noironetworks/neutron,mahak/neutron,eayunstack/neutron,huntxu/neutron,openstack/neutron,huntxu/neutron