Adapt SNAPSHOT plugin api example to the 3.1 version
Adapt SNAPSHOT plugin api example to the 3.1 version

Change-Id: I9d3b89d790ea6cd573d33c493d4224468c17fa82

GerritCodeReview/plugins_admin-console,GerritCodeReview/plugins_admin-console,GerritCodeReview/plugins_admin-console