Small bugs in 'nucmd package delete' command

[analogrelay]

There are three small bugs in the command. First, it doesn't create the "ng-backups" container if it does not already exist. This causes a 404 error.

Second, the deletion fails if the blob has any snapshots (which it may have due to package edits)

Third, it requires an environment even when all the values are pre-specified

Test Notes

Mostly small items that don't require a lot of verification. If you really want to verify something you could ensure that deletion works when all the connection strings are manually specified and nucmd.exe is run from outside the NuOps environment.