Rename instance_actions v3 to server_actions

* Renames the os-instance_actions v3 plugin to os-server-actions
* Also modifies api specific tests and expected user input JSON
* DocImpact only for v3 Nova api documentation for this plugin.

Closes-Bug: #1206032

DocImpact

Change-Id: Id5049e10f5ef540d0d8e3871d800e9d9cb33da73
Merge "Rename instance_actions v3 to server_actions"