Fix import errors in stop hook.

Fix import errors in stop hook.

This branch includes three trivial fixes:
- stop hook not working;
- using https://manage.jujucharms.com as charmworld URL by default;
- no need to provide credentials in sandbox mode.

https://code.launchpad.net/~frankban/charms/precise/juju-gui/bug-1171490-stop-hook/+merge/162149

(do not edit description out of merge proposal)

[frankban, 2013-05-02 16:31:26]

Please take a look.

[teknico, 2013-05-02 17:04:43]

LGTM, nice fixes and test.

[gary.poster, 2013-05-02 17:22:49]

LGTM, thank you!

[frankban, 2013-05-03 10:33:47]

*** Submitted:

Fix import errors in stop hook.

This branch includes three trivial fixes:
- stop hook not working;
- using https://manage.jujucharms.com as charmworld URL by default;
- no need to provide credentials in sandbox mode.

R=teknico, gary.poster
CC=
https://codereview.appspot.com/9125043

[frankban, 2013-05-03 11:02:07]

Thanks for the reviews, Gary and Nicola!
Merged trunk, deploy tests passed two times in a row.