If running git clean after reset then retry

* modules/jenkins/files/slave_scripts/gerrit-git-prep.sh
* .../openstack_project/files/jenkins_job_builder/config/macros.yaml
* .../infra-publications.yaml: If a git clean can not remove some
files, for example because a previous command has not freed its open
file handles, it will return nonzero. If this happens, wait a moment
and try again in case this is only a briefly transient problem.

Change-Id: If11320da7379c8fb8841b945067ce544188f5681
Merge "If running git clean after reset then retry"