Follow on to Ie17ef9ce1147cbaec2e42db932c7d59293b49b1b
Adds seed_deploy_containers_registry_attempt_login variable to seed.yml,
which acts as a redirection of deploy_containers_registry_attempt_login
so that the variable is more descriptive, declared in a better location,
and extensible to other groups
Change-Id: I86d8f13062ff8e664919cd5d63bc17bdafb32e0c
1476b9a68b