This patch adds a new microversion to
``GET /servers/{server_id}/os-instance-actions/{req_id}`` API to
include the ``host`` field for admin and an ``hostId`` for all users
by default. And the display of newly added ``host`` field will be
controlled by the same policy as the ``traceback`` field.
The newly added fields can be used to determine on which host a
given action event occurred.
Part of blueprint: add-host-to-instance-action-events
Change-Id: I2f8b4a12a088b9ed96b428eafde2e0c478fb1db5