Sync server_external_events v2 to v2.1 Part 1

This syncs commit I18062b81e50c722ec96b4296ac39384493683ae3 which
was made to the v2 version of os-server-external-events but not
the v2.1 version.

Partially implements blueprint v2-on-v3-api

Change-Id: If0657744fac021f635ce292142c82239751ae2f2
Merge "Sync server_external_events v2 to v2.1 Part 1"