rest-api: connect the crush_node views to API endpoints

Signed-off-by: Gregory Meno <gregory.meno@inktank.com>
tests: add tests for crush_nodes

Test that we generate the expected set of rados commands in the correct
order for each verb.
Test new crush data structures tracked by cthulhu
Add integration tests for the crush node endpoints: That things
requested can acutally be carried out
Fix rest_api url walking tests so we get included in the docs

Signed-off-by: Gregory Meno <gregory.meno@inktank.com>