Clarify os-stop API description
Clarify os-stop API description

The original changed description tried to explain the instance
data still exists after the API operation, but that was not clear.
This patch makes it clear as possible for users.
In addition, this patch removes the related sentence of os-start
to avoid the same confusion.

Change-Id: I46c4d24a67717807f4c6650a739f7855108783e9

klmitch/nova,jianghuaw/nova,klmitch/nova,gooddata/openstack-nova,klmitch/nova,mahak/nova,gooddata/openstack-nova,jianghuaw/nova,jianghuaw/nova,mahak/nova,gooddata/openstack-nova,openstack/nova,openstack/nova,gooddata/openstack-nova,jianghuaw/nova,rahulunair/nova,mikalstill/nova,rajalokan/nova,vmturbo/nova,Juniper/nova,rajalokan/nova,phenoxim/nova,rajalokan/nova,Juniper/nova,rajalokan/nova,openstack/nova,mahak/nova,phenoxim/nova,rahulunair/nova,mikalstill/nova,vmturbo/nova,vmturbo/nova,Juniper/nova,klmitch/nova,Juniper/nova,mikalstill/nova,rahulunair/nova,vmturbo/nova