Reset password, api version check.

[anastasiamac]

Description of change

Reset password functionality was only introduced on UserManager v2. This means that older juju controllers will not be able to provide this functionality when used with later clients.

This PR adds an API version check and ensures that api conection is closed after the command has run. Tests have been added and adjusted accordingly.

QA steps

1. Bootstrap an older version of Juju
2. Using newer client (develop tip), try to call 'change-user-password' with --reset option.

Documentation changes

n/a

Bug reference

n/a

[axw]

it was in the right place, in the block that created the client (NewUserManagerAPIClient). please move it back

[anastasiamac]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://ci.jujucharms.com/job/github-merge-juju