Remove improper NotFound except block in list servers

Added a couple tests to verify that NotFound was actually
never raised when no results are returned from list servers
or list servers details, and then removed the except blocks
from the controller.

Change-Id: I36856066b9e4c4e3f7b85ddf8facb35204034838
fixes: lp bug #1089385
Merge "Remove improper NotFound except block in list servers"