rename variables to "node_name"

ServiceObject is a complicated class, and also just happens to be
probably the most critical part of Crowbar's core engine.  So anything
we can do to make it more legible is a worthwhile investment.

This is a refactoring only, and should not affect behaviour in any way.
rename cryptic "elem" variable to "role_name"

ServiceObject is a complicated class, and also just happens to be
probably the most critical part of Crowbar's core engine.  So anything
we can do to make it more legible is a worthwhile investment.

This is a refactoring only, and should not affect behaviour in any way.
don't add deleted nodes to the run order (bnc#840255)

If a node is deleted but still associated with a proposal,
and then it is removed from that proposal and the proposal
applied, we need to avoid attempting to adjust the run list
for that node or attempting to run chef-client on that node.
Previously this would result in a

  undefined method `[]’ for nil:NilClass

crash, leaving all nodes stuck in the applying state, and
the proposal stuck in the committing state.

  https://bugzilla.novell.com/show_bug.cgi?id=840255

See also

  https://bugzilla.novell.com/show_bug.cgi?id=839714