[r=axwalk] Remove secrets-pushing for new bootstraps, API
- environs/BootstrapConfig now no longer removes
secret attributes from configuration. This is
on account of configuration not being populated
into cloud-init config now.
- juju/NewAPIConn now no longer pushes secrets,
as it is not necessary. This was not present in
1.16, so it is not a compatibility concern.
If we're okay with disabling new CLI from initialising
an old juju server, then we can also remove secrets
pushing from juju/NewConn. Doing this would allow us
to drop all notion of "secret attributes".
https://codereview.appspot.com/37090043/