This patch adds a new parameter ``locked_reason`` to
``POST /servers/{server_id}/action`` request where the
action is lock. It enables the user to specify a reason when locking
a server.
The locked_reason will be exposed through ``GET servers/{server_id}``,
``GET /servers/detail``, ``POST /servers/{server_id}/action`` where
the action is rebuild and ``PUT servers/{server_id}`` requests' responses.
The InstanceActionNotification will emit the locked_reason
along with the other instance details. This patch hence changes the
payload object to include the "locked_reason" field.
Note that "locked" will be allowed as a valid filtering/sorting parameter
for ``GET /servers/detail`` and ``GET /servers`` from this new microversion.
Implements blueprint add-locked-reason
Change-Id: I46edd595e7417c584106487123774a73c6dbe65e