Use BareMetal force_nodes in HEAT Template

Uses force-nodes described in the url below to
provision particular pieces of the HEAT template onto
particular baremetal machines.

https://review.openstack.org/#/c/27824/
Adds test for updating rack with resource_class_id

when resource_class_id is already there.
See #39 (https://github.com/tuskar/tuskar/issues/39)
Merge pull request #49 from petrblaho/test_for_rack_update_with_resource_class_id_issue_39

Adds test for updating rack with resource_class_id when resource_class_id is already there.
Merge pull request #46 from mtaylor/update_template_generations

Use BareMetal force_nodes in HEAT Template
Fix repo location in README
Fix updating racks collection on resource class

There were problems when some racks should be removed from the
resource class [1]. Now this is fixed and tests for this case are
added.

[1] https://github.com/tuskar/tuskar/issues/37
Remove stale fixme comment

The test now passes, so the comment can be removed.