Add initial files for tripleo in the gate.

Add jenkins job builder tripleo script (based on pbr).

Add prepare_node_tripleo.sh which will be called by nodepool.

Add prepare_tripleo.sh script, based on the devstack script
but pulling in just the tripleo repositories with pull-tools
tripleo-incubator script.

Add tripleo stanza to nodepool itself.

Update site.pp with variables for tripleo authentication.

Add experimental pipeline to zuul's layout.yaml for this job on
tripleo-incubator.

Change-Id: I03433d08585ba3a783fe939264d7521cafa83e41
Merge "Add initial files for tripleo in the gate."