This adds support for the node.resource_class field, introduced in
API 1.21. It can be modified on an existing node or passed when
creating a node, or used as a filter when fetching a list of nodes.
Change-Id: Id494a8b735a3532db84d90ba21da173f7e33ed1d
Depends-On: I936f2e7b2f4d26e01354e826e5595ff021c3a55c
Partial-Bug: #1604916