Improve Jenkins pipeline

Summary:
Skip the checkout stage, as implicit in Jenkins configuration.

Exclude Arc and Jenkins configuration file from the build.

Test Plan: https://cd.nasqueron.org/job/deploy-website-nasqueron-www1-www/9/artifact/

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2416