Only ship logs if LOGS_SERVER defined

When new projects are first being stood up they don't always have the
ability to pull their console logs since Jenkins may be in a locked down
mode. If this is the case then the log shipping will always fail and
cause the job to be marked as either FAILED or UNSTABLE. Instead we
should only ship the logs if LOGS_SERVER is defined in Jenkins flagging
that the console logs are publicly available.

Change-Id: I6fc162fec2d7c0cdc1a3785a8ec726d2430d5c96
Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>