[BUGFIX beta] Do not attempt to serialize undefined models.

If a routes model is undefined do not attempt to serialize it.

Previously, this would cause an error like: `Cannot call get with 'id'
on an undefined object.`.
remove cookbooks because we don't have vagrant
Merge pull request #3933 from rjackson/fix_serialize_on_missing_models

[BUGFIX beta] Do not attempt to serialize undefined models.
Remove Vagrant references from CONTRIBUTING.md.
Merge pull request #3939 from fivetanley/remove-cookbooks

remove cookbooks because we don't have vagrant
Merge pull request #3942 from rjackson/remove_vagrant_from_contrib

Remove Vagrant references from CONTRIBUTING.md.