Revert "suite: don't schedule follow-on summary job for an empty run"

This reverts commit a2b7c728964fb0064ba2a69818289caf723f09fc.
Make sed expressions safe to run multiple times

Also, make them ignore commented lines.
Merge pull request #96 from ceph/wip-fix-sudoers

Make sed expressions safe to run multiple times
Merge git://github.com/ceph/teuthology