Fix branch parameter in publications publish job.

* .../files/jenkins_job_builder/config/infra-publications.yaml: The
infra-publications-publish job used the wrong syntax to expand the
ZUUL_BRANCH parameter in its target, and as a result the literal
string '${ZUUL_BRANCH}' was being used as a directory name on the
remote FTP server. This corrects it so that content will be
published to the intended path.

Change-Id: I4e3ef9b10e9932246a10b0dea48c5ebd4884a680
Merge "Fix branch parameter in publications publish job."