relation-get output is problematic

[William Reade]

On Wed, 2012-05-09 at 13:09 -0700, Gustavo Niemeyer wrote:
> We have an important bug to fix in relation-get and a few other
> commands. 

Just to be explicit here, the various hooks tools fall into the
following categories:

No output:
 - juju-log
 - open-port
 - close-port
 - relation-set

So, none of these accept --format, --output, or --test.

Normal output:
 - config-get
 - relation-get
 - relation-ids
 - relation-list

Each of these accepts all the above flags.

Subtly different:
 - unit-get

...which is different only in that --test is basically meaningless:
unit-get is only ever run in the context of an actual running unit,
which is therefore guaranteed to have truthy values for private-address
and public-address. To expose --test on unit-get would imply that this
is not the case; and on principle I'm a little bit uncomfortable about
doing this.

It *would* be architecturally convenient to collect all these flags
together, but I would only want to do so if we had general agreement
that exposing a meaningless --test flag in this case was a reasonable
thing to do (either because we may one day extend unit-get to expose
potentially falsey values, or just in service of UI consistency).
Opinions?

Cheers
William