Debian: add puppet system user
Debian: add puppet system user

To avoid error messages like this:
Unable to set ownership to puppet:puppet for log file:
/home/zuul/workspace/puppet.log

we're adding the puppet user before running ./run_tests.sh

Change-Id: I0a00a7f41e700a3e503c1b98947803af47230678

openstack/puppet-openstack-integration,openstack/puppet-openstack-integration,openstack/puppet-openstack-integration