cmd/...: fix single-key config commands

[axw]

Description of change

Fix controller-config and model-config commands
so that when a single key is specified, by
default we will format the value in its raw
form. Internally, we use the "smart" formatter
to do this.

To do this in a way that users can still get
YAML/JSON formatting of single keys as needed,
we introduce and default to tabular formatting
of controller config as we do for model config.

Also, fix the model-config command to honour
the -o/--output flag when a single key is
specified.

QA steps

1. juju bootstrap localhost
2. juju controller-config ca-cert (should print ca-cert without YAML multi-line prefix)
3. juju controller-config --format=yaml ca-cert (should print ca-cert with YAML multi-line prefix)
4. juju controller-config (should print attributes in tabular format)
5. juju model-config http-proxy="abc
   def"
6. juju model-config --output=/tmp/config.txt http-proxy (contents of /tmp/config.txt should be:

abc
def

Documentation changes

Default format of controller-config has changed, and for single-key format of model-config. We do not guarantee stability of the default formats, you must specify YAML/JSON for that.

Bug reference

Fixes https://bugs.launchpad.net/juju/+bug/1661506

[axw]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju