This avoids the conflict with the zuul user (1000) on the test
nodes. The executor will continue to use the default username
of 'zuul' as the ansible_user in the inventory.
This change also touches the zk and nodepool deployment to use
variables for the usernames and uids to make changes like this
easier. No changes are intended there.
Change-Id: Ib8cef6b7889b23ddc65a07bcba29c21a36e3dcb5
09935ff328