When 1 node besides the master node exists and is deleted, then any jobs that
were assigned to it cannot be re-assigned without editing the config.xml file
directly.

Steps to reproduce:
1. Create 1 (and only 1) node (excluding the master node).
2. Assign a job to the new node.
3. Delete the node.
4. Attempting to run the job fails because the node is missing and there isn't
any way to alter it now from the job configuration page.

Possible Solution:
1. Ensure the node selection option is still available on the job
configuration page even when no other nodes beside the master are available.
2. Default a job back to the master node when the node is was assigned to is
missing.

Note that this error is valid if there is only 1 node besides the master node
and it is deleted.