Description of problem:

In the web UI we would like have the Lab Controller drop down to NOT include the option of picking a lab controller that was removed from beaker.  Having them on the pick list only gives the users an option to pick a lab controller that is no longer around.

Version-Release number of selected component (if applicable):

22.1

How reproducible:

100%

Steps to Reproduce:
1. Select any beaker system in the Web UI for beaker that you have the rights to edit.
2. Click on the "Essentials" tab
3. Go to the "Lab Controller" drop down
4. Select a lab controller from the list and as you can see there is a list of all the lab controllers in the environment both active and removed. 

Actual results:

The user is allowed to pick a lab controller that has been removed from the environment.

Expected results:

Users should not be able to pick a lab controller that has been removed as no beaker job will run against a non-active / non-existing lab controller.

Additional info:

If the list of lab controllers can _not_ be hidden from the pick list, would it be possible to add something next to the entries that should be hidden that the status of the lab controller is removed.  That way user will know not to pick a lab controller that has been removed.