Use charm store API to retrieve GUI revision.

Use charm store API to retrieve GUI revision.

This branch includes the following small fixes
in preparation for the 1.6 release:

- bump version up to 1.6.0;
- use the charm store API to retrieve the URL
  of the last revision of the juju-gui charm;
- add initial support for vivid: the new series can now
  be selected as default bootstrap node series when
  creating/editing environments.

  Tests: `make check`.

  QA:
  - just run `.venv/bin/python juju-quickstart` as
    usual, locally and on a ec2 environment
    (it would be nice if both precise and trusty 
    are used as default series in this QA); check
    that vivid can be added as a default-series
    in the environment edit view; check that 
    the last Juju GUI revision is correctly retrieved.

https://code.launchpad.net/~frankban/juju-quickstart/initial-vivid-support/+merge/246199

(do not edit description out of merge proposal)

[frankban, 2015-01-12 17:54:33]

Please take a look.

[martin.hilton, 2015-01-12 18:02:13]

LGTM, No QA (yet)

[martin.hilton, 2015-01-12 19:46:50]

On 2015/01/12 18:02:13, martin.hilton wrote:
> LGTM, No QA (yet)

QA OK

[rog, 2015-01-13 09:44:25]

On 2015/01/12 19:46:50, martin.hilton wrote:
> On 2015/01/12 18:02:13, martin.hilton wrote:
> > LGTM, No QA (yet)
> 
> QA OK

LGTM

[frankban, 2015-01-13 09:48:19]

*** Submitted:

Use charm store API to retrieve GUI revision.

This branch includes the following small fixes
in preparation for the 1.6 release:

- bump version up to 1.6.0;
- use the charm store API to retrieve the URL
  of the last revision of the juju-gui charm;
- add initial support for vivid: the new series can now
  be selected as default bootstrap node series when
  creating/editing environments.

  Tests: `make check`.

  QA:
  - just run `.venv/bin/python juju-quickstart` as
    usual, locally and on a ec2 environment
    (it would be nice if both precise and trusty 
    are used as default series in this QA); check
    that vivid can be added as a default-series
    in the environment edit view; check that 
    the last Juju GUI revision is correctly retrieved.

R=martin.hilton, rog
CC=
https://codereview.appspot.com/197740043

[frankban, 2015-01-13 09:48:55]

Thanks for the reviews!