cbbackupmgr backup -resume fails if user not a full administrator

Problem
When a user that has backup and restore permissions does a backup and it fails mid way through and the user resumes the backup again it will fail with invalid authentication beacuse cbbackupmgr is using pre 5.0.0 auth

Steps to reporduce
1. Set up a cluster 5.0+ (tested in 5.5.0 6.0.0 and mad-hatter)
2. Add a user with data backup and restore permissiosn
3. Create a bucket and add some data
4. Backup the data but before it finish cancle the backup by using control c
5. Now try a resume

this should fail with an error similar to:

Error backing up cluster: authentication error

Expectation
That if a user can take a backup it should also be able to resume said backup