Refactor AWS+vCenter deletion exception

[alonagetzler]

in case an app was deployed and then the VM was deleted from AWS/vCenter we should throw exception/result that the server will be able to identify when running the "Delete" command, so when deleting a deployed app from cloudshell which points to a VM that doesn't exist anymore the server will know to continue with the deletion (in 7.1 we hardcoded the error description to solve this)

note - we need to update Shay's scrum once this refactor is done so they'll refactor the server accordingly

[alonagetzler]

maybe we should think about custom exceptions in general and how we treat them in CloudShell, not just this specific deletion exception (something in the shell core)
need to setup a meeting with Roni, Shay & Ronen prior to starting the work on this story