Comment 16 for bug 1452680

--upload-tools is a developer hack that has proven to be very dangerous in production environments. While to gives repeatability during bootstrap, it does so by increasing the unknowns for future upgrades.

1. the agent deployed is not in streams, it is treated as development version without an upgrade path.
2. Users must use --upload-tool when upgrading, but that is based on the client.
   We have seen that enterprises are running more than one version of the client, and some are
   development versions, which make unpredictable choices for an upgrade to a production env.
3. --upload-tools disabled streams
   Users need to configure streams to get back to "just works"
       juju set-env agent-metadata-url=https://streams.canonical.com/juju/tools

By setting agent-version in the config, users can guarantee repeatability in bootstraps and upgrades.

Since juju is designed to upgrade to fix importance issues in clouds and in the state-server, anything that automates it needs to choose to state the version required, or wait for upgrades to complete.