Upgrade from 2.6.x to 2.7.0 fails when cleaning sparse loop volumes

[gdemonet]

Component: salt, upgrade, storage

Summary:

When running the upgrade.sh script to upgrade a MetalK8s 2.6.x cluster to 2.7.0, the Upgrading all nodes one by one step will abort for each node which has no SparseLoopDevice Volume provisioned, during the metalk8s.volumes.cleanup state execution. It will show an error similar to:

                        ID: Cleanup existing loop devices                                                                                                                                                                                     
                  Function: salt.state                                                                                                                                                                                                        
                    Result: False                                                                                                                                                                                                             
                   Comment: Run failed on minions: metalk8s-control-plane-02                                                                                                                                                                  
                   Started: 23:39:50.586427                                                                                                                                                                                                   
                  Duration: 2838.153 ms                                                                                                                                                                                                       
                   Changes:                                                                                                                                                                                                                   
                            metalk8s-control-plane-02:                                                                                                                                                                                        
                                Data failed to compile:                                                                                                                                                                                       
                            ----------                                                                                                                                                                                                        
                                Rendering SLS 'metalk8s-2.7.0:metalk8s.volumes.cleanup' failed: Jinja variable 'target_is_2_7' is undefined 

The only available workaround is to restart the upgrade.sh script, once per failing node, until completion.

[gdemonet]

This issue was fixed in #3048.