An operator might want to ensure Swift is available during
an upgrade and manually upgrade Swift on completion of the
maintenance.
The operator would need to set these vars before operation:
export SKIP_SWIFT_UPGRADE=yes
export CONTAINERS_TO_DESTROY=add_!swift_all_exclusion
This would prevent the swift containers from being torn
down during the upgrade and would skip all Swift upgrade
operations.
Change-Id: Ibf40499750751dd9f41e447b7b90bb77f592cc14