Docker images currently based on ci-jessie; either delete, or migrate:
- php55
- composer-php55
- composer-test-php55
- composer-php55
- php56
- composer-php56
- composer-test-php56
- composer-php56
- hhvm-jessie Gerrit 518304
- lintr Gerrit 523834 and Gerrit 523835
- npm: T211784: Upgrade all CI jobs from node6/npm3 to node10/npm6 across all projects
- quibble-jessie Gerrit 518302
- zuul-cloner Gerrit 518241 and Gerrit 518297
- ci-jessie (very last usages were for releng/npm and releng/npm-stretch which were nodejs6/npm3.