Update "SHUTOFF" description in API guide
Update "SHUTOFF" description in API guide

Two things are updated here:

1. The SHUTOFF status from the API is for any stopped server,
   regardless of whether or not it was stopped via the REST API
   or the sync_instance_power_state periodic task in the compute.

2. Remove the mention of the "shutdown_terminate" flag since that
   was only ever implemented in the legacy v2 API for EC2
   compatibility and it wouldn't actually work now with the v2.1
   server create schema anyway.

Change-Id: I97071be164d15298fa2a5a7374a8ba8235d188e4
Related-Bug: #1722403

klmitch/nova,rahulunair/nova,gooddata/openstack-nova,mahak/nova,phenoxim/nova,gooddata/openstack-nova,klmitch/nova,mahak/nova,mikalstill/nova,rahulunair/nova,rahulunair/nova,openstack/nova,klmitch/nova,mikalstill/nova,phenoxim/nova,gooddata/openstack-nova,mahak/nova,klmitch/nova,mikalstill/nova,gooddata/openstack-nova,openstack/nova,openstack/nova