Describe the enhancement:

An agent upgrade command needs some form of retry mechanism as discussed in #752
This retry mechanism should work for scheduled actions (may retry within the upgrade window), and other actions (given a default time frame or number of attempts).

The action queue may need to be (re) used for this.

Describe a specific use case for the enhancement or feature:

An upgrade may fail due to temporary network issues. In this case we would expect the upgrade to try again later and succeed.

Currently the upgrade process will remove all non-current version artifacts from the downloads directory when starting the upgrade process; so this may redownload a (verified) artifact