Move openstack-specific config out of ::jenkins

The ::jenkins::slave class contained a lot of openstack-specific
configuration rather than configuration of a generic jenkins slave.

The term "bare slave" is overloaded and confusing: create simple_slave
and thick_slave to differentiate between the two meanings of "bare".
Some portions of ::jenkins::slave will move to simple_slave, some
portions to thick_slave, and some portions to slave_common (all in the
openstack_project module).

Change-Id: I5281a03a7f6da3f98714bcc59ae840ace8435578
Merge "Move openstack-specific config out of ::jenkins"