Add IsLXCSupported()
Added tests

Added tests for the following cases:

* Mallformed cgroup file
* Missing cgroup file
* system juju is running on is not linux
use filetesting
Responded to feedback
Refactor the UserManager and commands.

This branch adds consistency to the UserManager.
Primarily around the use of tags to pass the usernames.
Also untangles the API client from the server that was
there with the user manager structs being defined in the
apiserver package (not params).

The commands have been hooked up, and tested manually.

There were several clear changes needed when testing:
 * until we have multiple environments, creating a user
   should cause that user to have access to the environment
 * when adding a user, we should always write out the jenv
   file (until the user is able to login and see themselves)
 * the remove user command has been renamed to disable,
   as it wasn't removing the user at all (this is still todo)
Merge branch 'user-manager-tag-redux' into juju-user-list
Add a method to state to get all the users.
Add apiserver changes to return all users.
Add a list command for users and hook it up.
merge trunk
More refactoring.
Hook it up.
Update the state package with the correct factory args.
Update test.
Tweaks for review comments.
simplify constants
Rename InitialEnvironment to StateServerEnvironment.
Added Actions API client: ServiceCharmActions
Added Actions API client: ServiceCharmActions

Updated tests and return type for api/actions ServiceCharmActions.
Added Actions API client: ServiceCharmActions

Updated error catching for ServiceCharmActions and added test