ci-dockerfiles-sanity-check: Build name fix for non-Gerrit case

If there's no Gerrit patch, don't add dangling hyphen to build name.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I95d4520c3d0588ff657d4dbd7377816174091acf
1 file changed