Show logs for DB initialization and migration for Auto DevOps

Continuing from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21955

Due to helm not supporting hook logs, this MR does not show the logs from the intialization and migration logs.

It is inconvenient to have to find the right pods to gather the logs. As a workaround, one can run :

• kubectl logs -n $KUBE_NAMESPACE -l job-name=$CI_ENVIRONMENT_SLUG-db-initialize
• kubectl logs -n $KUBE_NAMESPACE -l job-name=$CI_ENVIRONMENT_SLUG-db-migrate