Add sequence diagrams to resize/cold migrate contrib doc
Add sequence diagrams to resize/cold migrate contrib doc

This adds high level sequence diagrams for the resize flows
including confirm and revert.

Change-Id: Iaca4325c9b4d7b63c5bc811bdba2db0d10db61f6

openstack/nova,klmitch/nova,mahak/nova,klmitch/nova,openstack/nova,mahak/nova,openstack/nova,rahulunair/nova,mahak/nova,rahulunair/nova,klmitch/nova,klmitch/nova,rahulunair/nova