Port fping extension to work in v2.1/v3 framework

Ports v2 fping extension and adapts it to the v2.1/v3 API
framework. API behaviour is identical.

- unittest code modified to share testing with both v2/v2.1
- Adds expected error decorators for API methods

Partially implements blueprint v2-on-v3-api

Change-Id: I8dc4ede46826bf6062097a3b4ba6be9a09a1bd12
Merge "Port fping extension to work in v2.1/v3 framework"