Ported r2559 from trunk to 1.18

Ported r2559 from trunk to 1.18

For the deploy and upgradecharm commands, when a series is not provided, and a
default-series is not set in the environment config, the client will resolve
the series with the charm store, through the state server. If the client is
working with a 1.16 state server, it will resolve the series directly with the
charm store.

Existing environments will have a default-series, so they should have no
change in series selection.

New environments will continue to support the default-series config setting,
but it can be omitted, and is not set by default.

https://code.launchpad.net/~cmars/juju-core/1.18-resolve-cs-series/+merge/214097

(do not edit description out of merge proposal)

[cmars, 2014-04-03 19:20:56]

Please take a look.

[cmars, 2014-04-03 19:30:29]

This is a cherry-pick of r2559 from trunk.

Original trunk proposal, for context: https://codereview.appspot.com/80280043/

PTAL & thanks,
-Casey

[wallyworld, 2014-04-03 23:19:37]

Cherry pick looks ok.
Only reviewed for obvious backporting errors as original work was approved.

[cmars, 2014-04-09 22:49:16]

Please take a look.

[cmars, 2014-04-09 22:51:29]

On 2014/04/09 22:49:16, cmars wrote:
> Please take a look.

lbox picked up the wrong branch here, please ignore.