Add placement API methods for testing routed provider nets

Routed provider networks feature uses the placement API, to test the
feature we need to add the following client methods to the placement
client:
* list_resource_providers
* show_resource_provider
* list_resource_provider_inventories
* list_resource_provider_aggregates

Change-Id: I4e4b104bf4b6b26b02d95b2c9697f4bfdba25ac4
5 files changed