cmd/juju/{ssh,debughooks}.go: restore 1.16 compat

cmd/juju/{ssh,debughooks}.go: restore 1.16 compat

This addresses bug #1253639. It makes it so that "juju ssh" "juju scp"
and "juju debug-hooks" are again compatible with 1.16.

I audited against a live 1.16.3 install that you can:
  juju ssh 0
  juju scp 0:/var/log/juju/machine-0.log .
  juju debug-hooks mysql/0
  juju debug-hooks mysql/0 master-relation-departed

All of which you couldn't do in trunk. (the actual ssh process was
switched to use Client.PublicAddress which affected everything, and
debug-hooks with a relation name used Client.ServiceCharmRelations.)

These aren't strictly just coping the code that was in 1.16 into trunk
and using it, but that is because it involves the middle piece of a
multi-step process. (vs things like destroy-machine that is just a
single API call that we do differently.)

The one "functional" change here is that if you run "juju debug-hooks
mysql/0 XXXX" with a relation hook that doesn't actually exist, it now
logs at INFO level the list of possible relation hooks. So you can see
the list with "--debug". I can revert that easily, but it was *really*
helpful when trying it out. The list can get really long, so I can
understand not showing it by default.

https://code.launchpad.net/~jameinel/juju-core/1.17-client-public-address-compat-1253639/+merge/196873

(do not edit description out of merge proposal)

[jameinel, 2013-11-27 12:11:06]

Please take a look.

[axw, 2013-11-28 05:06:24]

LGTM with fix to log

https://codereview.appspot.com/33860043/diff/1/cmd/juju/debughooks.go
File cmd/juju/debughooks.go (right):

https://codereview.appspot.com/33860043/diff/1/cmd/juju/debughooks.go#newcode125
cmd/juju/debughooks.go:125: logger.Infof("unknown hook %s, valid hook names:
%v", c.Target, names)
s/c.Target/hook/?

[jameinel, 2013-11-28 12:01:24]

Please take a look.

https://codereview.appspot.com/33860043/diff/1/cmd/juju/debughooks.go
File cmd/juju/debughooks.go (right):

https://codereview.appspot.com/33860043/diff/1/cmd/juju/debughooks.go#newcode125
cmd/juju/debughooks.go:125: logger.Infof("unknown hook %s, valid hook names:
%v", c.Target, names)
On 2013/11/28 05:06:24, axw wrote:
> s/c.Target/hook/?

Done.