Port Simple_tenant_usage API to v3 Part 2

This patch contains the changes required to adapt the Simple_tenant_usage
extension and the corresponding unittest to the v3 framework

Partially implements: bp v3-api-extension-versioning

Change-Id: I2db66704a77e822543e270773acc847267ef6ece
Merge "Port Simple_tenant_usage API to v3 Part 2"