Redo slave manifests for clarity and correctness.

The differences between openstack_project::slave,
openstack_project::slave_template, and openstack_project::bare_slave
were not always clear. Keep openstack_project::slave as the default long
running slave manifest, but replace slave_template with a
single_use_slave.pp to make it clear where single use slave config
begins. Add the ability to toggle automatic upgrades and jenkins sudo
rights to this new manifest. Finally, add a more verbose comment to
bare_slave explaining what it is useful for (having a jenkins like slave
host that doesn't need a firewall or ntp or automatic upgrades).

Change-Id: I3989c9e6ad9469f441ca5d3627f7b3b704d8a8da
Merge "Redo slave manifests for clarity and correctness."