Change exception type from HTTPBadRequest to HTTPForbidden

When user without admin permission wants to get a list of servers
which are in 'deleted' state, currently it raises  HTTPBadRequest.
This should be changed to HTTPForbidden exception.

Change-Id: I29da5f055c69e8aba66ffb068a3601ae69b2fc94
Closes-Bug: #1281904
Merge "Change exception type from HTTPBadRequest to HTTPForbidden"