Switch Jenkins containers to the jenkins/jenkins image

Summary:
The jenkinsci/jenkins image has been deprecated.

Both LTS and weekly versions are now provided
by the jenkins/jenkins repository.

References:

• https://github.com/jenkinsci/docker/issues/515 (jenkinsci/jenkins)
• https://github.com/jenkinsci/docker/pull/517 (jenkinsci → jenkins)

Test Plan: Respin Jenkins containers

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1828