Fix gerrit-push-patch Job key not in trailers

Fix gerrit-push-patch Job key not in trailers

Key-value pairs in Git should be appended to the Git trailers section
(AKA footer). This patch fixes the commit message produced by
gerrit-push-patch which currently creates a commit message where the
Job key appears in the commit message body rather than the trailer.

For example:

    An example commit message

    Job: builder-job/123

    Change-Id: 1234567
    Signed-off-by: Jenkins <jenkins@example.org>
This fixes it to:

    An example commit with proper trailer

    Job: builder-job/123
    Change-Id: 123457
    Signed-off-by: Jenkins <jenkins@example.org>
Signed-off-by: Thanh Ha <zxiiro@gmail.com>
Change-Id: I66c9b0813b36065c20adcf0e886eaa29354ca603