refactor to remove apiRootForEntity

refactor to remove apiRootForEntity

This was going to be used for giving different roots for differnt enitities, but we don't actually do that, and it made for some very awkward code.

https://code.launchpad.net/~natefinch/juju-core/jameinel-pinger-for-agent/+merge/217836

(do not edit description out of merge proposal)

[natefinch, 2014-04-30 22:02:31]

Please take a look.

[rog, 2014-05-01 00:58:21]

I'd much prefer it if we actually completed the TODO and returned an
entity-specific API root. It's not that difficult to do.

[fwereade, 2014-05-06 08:29:04]

On 2014/05/01 00:58:21, rog wrote:
> I'd much prefer it if we actually completed the TODO and returned an
> entity-specific API root. It's not that difficult to do.

I have some sympathy here, but (1) we haven't done it yet (2) we're going to
consolidate the agents anyway, rendering its expected value somewhat lower and
(3) eventually we're going to have to open up client access from the agents
anyway (for service-level -- and eventually stack-level -- orchestration), and
at that point it'll only be harder to do so if we need to unpick that sort of
logic.

ie it's simpler now, and it's likely to stay this simple in the future; and
we'll always have to carry the cost of carefully fine-grained permissions in
client *anyway*. And we can still easily prevent access to agent APIs from
clients at the facade level anyway. So, LGTM, and thanks.