This does a few things:
1. Fixes the "migration_status" wording since that does not
exist and could be confused as a field on the server
resource which it is not, it is referring to the migration
resource status.
2. Fixes the RESIZED status mention since that is not a real
server status, it probably meant VERIFY_RESIZE (RESIZED is
the name of the nova.compute.vm_states variable used in the
code to set the VERIFY_RESIZE status in the API).
3. Adds words about options to correct the server status from
ERROR after confirmResize fails, the most obvious being
an admin resetting the server status to ACTIVE or the user
hard rebooting the server.
Change-Id: I7de257ad78031d137616d724bee3fa1cbf40d6fa
Related-Bug: #1821594
4d0aab16ec