Only Submit Security Scan Results that Exist

Only Submit Security Scan Results that Exist

When anteater runs it generates a shortlog containing any errors that
were encountered during it's run.

If no errors exist it will still create an empty file 'shortlog'. A
review containing no content will be attempt to be posted and fail with:

  fatal: Argument "{COMMIT | CHANGE,PATCHSET}" is required

Instead of attempting to post nothing, the job should just skip
submitting a review.

Change-Id: I3feacb15e47dea204783053b3e67a9aa81ba164d
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>